Photosensitive resin compositive for printing plate precursor capable of laser engraving

ABSTRACT

Disclosed is a photosensitive resin composition for forming a laser engravable printing element, comprising: (a) 100 parts by weight of a resin which is a plastomer at 20° C., wherein the resin has a number average molecular weight (Mn) of from 1,000 to 100,000 and has a polymerizable unsaturated group in an amount such that the average number of the polymerizable unsaturated group per molecule is at least 0.7, (b) 5 to 200 parts by weight, relative to 100 parts by weight of resin (a), of an organic compound having an Mn of less than 1,000 and having at least one polymerizable unsaturated group per molecule, and (c) 1 to 100 parts by weight, relative to 100 parts by weight of resin (a), of an inorganic porous material. Also disclosed is a laser engravable printing element formed from the above-mentioned resin composition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photosensitive resin composition forforming a laser engravable printing element. More particularly, thepresent invention is concerned with a photosensitive resin compositionfor forming a laser engravable printing element, comprising: (a) a resinwhich is a plastomer at 20° C., wherein the resin has a number averagemolecular weight of from 1,000 to 100,000 and has a polymerizableunsaturated group in an amount such that the average number of thepolymerizable unsaturated group per molecule is at least 0.7, (b) anorganic compound having a number average molecular weight of less than1,000 and having at least one polymerizable unsaturated group permolecule, and (c) an inorganic porous material. By the use of thephotosensitive resin composition of the present invention, it becomespossible to produce a printing element which not only has highuniformity in thickness and high dimensional precision, but alsogenerates only a small amount of debris during the laser engraving ofthe printing element. Further, the produced printing element isadvantageous in that a precise image can be formed on the printingelement by laser engraving and the resultant image-bearing printingplate has small surface tack. Further, the present invention is alsoconcerned with a laser engravable printing element formed from thephotosensitive resin composition of the present invention.

2. Prior Art

The flexographic printing method is used in the production of packagingmaterials (such as a cardboard, a paperware, a paper bag and a flexiblepackaging film) and materials for construction and furnishing (such as awall paper and an ornamental board) and also used for printing labels.Such flexographic printing method has been increasing its importanceamong other printing methods. A photosensitive resin is generallyemployed for producing a flexographic printing plate, and the productionof a flexographic printing plate using a photosensitive resin hasconventionally been performed by the following method. A photo-maskbearing a pattern is placed on a liquid resin or a solid resin sheet(obtained by molding a resin into a sheet), and the resultant maskedresin is imagewise exposed to light, to thereby crosslink the exposedportions of the resin, followed by developing treatment in which theunexposed portions of the resin (i.e., uncrosslinked resin portions) arewashed away with a developing liquid. Recently, the so-called “flexo CTP(Computer to Plate) method” has been developed. In this method, a thin,light absorption layer called “black layer” is formed on the surface ofa photosensitive resin plate, and the resultant resin plate isirradiated with laser to ablate (evaporate) desired portions of theblack layer to form a mask bearing an image (formed by the unablatedportions of the black layer) on the resin plate directly withoutseparately preparing a mask. Subsequently, the resultant resin plate isimagewise exposed to light through the mask, to thereby crosslink theexposed portions of the resin, followed by developing treatment in whichthe unexposed portions of the resin (i.e., uncrosslinked resin portions)are washed away with a developing liquid. Since the efficiency forproducing the printing plates has been improved by this method, its useis beginning to expand in wide variety of fields. However, this methodalso requires a developing treatment as in the case of other methodsand, hence, the improvement in the efficiency for producing the printingplates is limited. Therefore, it has been desired to develop a methodfor forming a relief pattern directly on a printing element by using alaser without a need for a developing treatment.

As an example of a method for producing a printing plate by directlyforming a relief pattern on a printing element using laser, which doesnot require the developing treatment, there can be mentioned a method inwhich a printing element is engraved directly with laser. Such a methodis already used for producing relief plates and stamps, in which variousmaterials are used for forming the printing elements.

In the following specific examples of the above-mentioned method forproducing a printing plate (by directly forming a relief pattern on aprinting element using laser), the term “printing element” means anelement prior to the engraving with laser, and the “printing plate”means a plate obtained by engraving the printing element with laser toform a relief pattern on the printing element.

Examined Japanese Patent Publication No. Sho 47-5121 (corresponding toU.S. Pat. No. 3,549,733) discloses the use of a polyoxymethylene orpolychloral for producing a printing element. Further, Japanese PatentApplication prior-to-examination Publication (Tokuhyo) No. Hei 10-512823(corresponding to DE 19625749 A) describes the use of a silicone polymeror silicone fluoropolymer for producing a printing element. In each ofthe specific examples of compositions used for producing the printingelement, which are described in this patent document, fillers, such asamorphous silica, are added to the above-mentioned polymer. However, aphotosensitive resin is not used in the inventions disclosed in theabove-mentioned patent documents. In the above-mentioned Japanese PatentApplication prior-to-examination Publication (Tokuhyo) No. Hei10-512823, amorphous silica is added to the polymer for enhancing themechanical properties of the polymer and reducing the amount of anexpensive elastomer used in the printing element. Further, this patentdocument has no description about the morphology of the amorphous silicaused.

Unexamined Japanese Patent Application Laid-Open Specification No.2001-121833 (corresponding to EP 1080883 A) describes the use of amixture of a silicone rubber and carbon black for producing a printingelement, wherein the carbon black is used as a laser beam absorber.However, a photosensitive resin is not used in this invention.

Unexamined Japanese Patent Application Laid-Open Specification No.2001-328365 discloses the use of a graft-copolymer as a material forproducing a printing element. Further, this patent document describesthat, for improving the mechanical properties of the graft copolymer,inorganic silica having a particle diameter which is smaller than thewavelength of the visible light may be mixed with the graft copolymer.However, this patent document has no description about the removal ofliquid debris which is generated by laser engraving. Further, in theWorking Examples of this patent document, a sheet of a photosensitiveresin was formed from a liquefied photosensitive resin which had beenprepared by adding a solvent to the resin; however, the production ofsuch a sheet is disadvantageous in that it was necessary to remove thesolvent by drying. In addition, the production of the above-mentionedsheet has drawbacks in that the working environment which is appropriatefor the use of a solvent must be maintained and that the completeremoval of solvent from the inside of the produced printing element isdifficult when the thickness of the printing element is in the order ofseveral millimeters.

Unexamined Japanese Patent Application Laid-Open Specification No.2002-3665 uses an elastomer composed mainly of ethylene monomer units,and this patent document describes that silica may be added to theelastomer as a reinforcing agent. In the Working Examples of this patentdocument, 50 parts by weight of porous silica and 50 parts by weight ofcalcium carbonate were added to 100 parts by weight of a resin. Both ofthe above-mentioned porous silica and calcium carbonate were used onlyas white reinforcing agents and, for achieving a satisfactoryreinforcing effect, those reinforcing agents were used in large amounts(total amount of the reinforcing agents was as large as 100 parts byweight). That is, the use of silica in this patent document does notextend beyond the customary use as a reinforcing agent. Further, theresin used in this patent document is not a photosensitive resin and theresin is cured by heating. Therefore, the curing rate of the resin islow and the dimensional precision of a sheet obtained from the resin ispoor.

DE 19918363 A discloses an invention in which a printing element isproduced from a polymer produced from recycled materials. This patentdocument describes not only a heat curable resin, but also aphotosensitive resin. In the single Example of this patent document, aresin composition containing a heat curable resin and carbon black isused. The addition of even a small amount of carbon black to a resinleads to a lowering of the light transmittance of the resin. Thus, it isimpossible to cure a resin composition (such as produced in the singleExample of DE 19918363 A) containing more than 1% by weight of carbonblack from the outer portion thereof through the inner portion thereof.Therefore, such a resin composition is not suitable for use in theproduction of a laser engravable printing element. The lowering of thecurability of a resin by the addition of carbon black markedly occursespecially when a liquid photosensitive resin is used. Further, thispatent document has no description about either an inorganic porousmaterial other than carbon black or the removal of liquid debrisgenerated by laser engraving.

Each of Japanese Patent No. 2846954 (corresponding to U.S. Pat. No.5,798,202) and Japanese Patent No. 2846955 (corresponding to U.S. Pat.No. 5,804,353) discloses the use of a reinforced elastomer materialobtained by mechanically, photochemically and thermochemicallyreinforcing a thermoplastic elastomer, such as SBS(polystyrene-polybutadiene-polystyrene), SIS(polystyrene-polyisoprene-polystyrene) and SEBS(poly-styrene-polyethylene/polybutadiene-polystyrene). When a printingelement formed from a thermoplastic elastomer is engraved with a laserbeam having an oscillation wavelength within the infrared region, evenportions of the printing element which are distant from the portionirradiated with the laser beam also tend to be melted by heat.Therefore, the resultant printing element cannot be used for preparingan engraved pattern having a high resolution. For removing this problem,it is necessary to add a filler to the thermoplastic elastomer tothereby enhance the mechanical properties thereof. In each of theabove-mentioned patent documents, for enhancing the mechanicalproperties of the thermoplastic elastomer and improving the absorptionof the laser beam by the thermoplastic elastomer, carbon black havingexcellent ability to enhance the mechanical properties of a resin isadded to a thermoplastic elastomer. However, since carbon black is addedto the elastomer, light transmittance of the elastomer is lowered, whichis disadvantageous when it is attempted to crosslink the elastomer byirradiation (i.e., when it is attempted to perform a photochemicalreinforcement of the elastomer). Therefore, when the above-mentionedreinforced elastomer material is subjected to laser engraving, itresults in a generation of a large amount of debris (including viscousliquid material) which is difficult to remove. The generation of suchdebris not only necessitates a time-consuming treatment for removing thedebris, but also causes problems, such as the imprecise boundary betweenelastomer portions which have been melted by laser beam irradiation andunmolten elastomer portions which form the relief pattern, the swellingof the edges of the unmolten elastomer portions forming the reliefpattern, the adherence of the molten elastomer to the surfaces and/orsides of the unmolten elastomer portions forming the relief pattern, andthe destruction of portions of the relief pattern which correspond tothe dots of a print obtained using the relief pattern.

Further, when a large amount of liquid debris, which is presumed to be alaser decomposition product of the resin, is generated during the laserengraving of the printing element, the liquid debris stains the opticalparts of a laser engraving apparatus. When the liquid debris is attachedto the surface of optical parts, such as a lens and a mirror, the resincauses serious troubles of the apparatus, such as burnout of theapparatus.

As apparent from the above, various materials for laser engraving havebeen proposed. However, a material for forming a laser engravableprinting element, which not only has high uniformity in thickness andhigh dimensional precision, but also enables easy laser engravingwithout suffering problems caused by the generation of debris, has notyet been realized.

SUMMARY OF THE INVENTION

In this situation, the present inventors have made extensive andintensive studies with a view toward developing a photosensitive resincomposition which is suitable as a material for forming a printingelement used for producing an image-bearing printing plate, wherein theimage-bearing printing plate is produced by removing a part of theprinting element by laser beam irradiation. As a result, it hassurprisingly been found that, when a printing element is formed from aspecific resin composition which comprises a photosensitive resin (whichis easily decomposed by laser beam irradiation) and an inorganic porousmaterial (which is used for absorption removal of viscous liquid debrisgenerated in a large amount due to the use of the easily decomposableresin), the formed printing element not only has high uniformity inthickness and high dimensional precision, but also generates only asmall amount of debris during the laser engraving of the printingelement. Further, the formed printing element is advantageous in that aprecise image can be formed on the printing element by laser engravingand the resultant image-bearing printing plate has small surface tack.The present invention has been completed, based on these novel findings.

Accordingly, it is an object of the present invention to provide aphotosensitive resin composition which is especially advantageous foruse in the production of a relief printing plate, which production isconventionally accompanied by a generation of a large amount ofengraving debris.

It is another object of the present invention to provide a laserengravable printing element formed from the above-mentioned resincomposition.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description takenin connection with the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect of the present invention, there is provided aphotosensitive resin composition for forming a laser engravable printingelement, comprising:

(a) 100 parts by weight of a resin which is a plastomer at 20° C.,wherein the resin has a number average molecular weight of from 1,000 to100,000 and has a polymerizable unsaturated group in an amount suchthat-the average number of the polymerizable unsaturated group permolecule is at least 0.7,

(b) 5 to 200 parts by weight, relative to 100 parts by weight of theresin (a), of an organic compound having a number average molecularweight of less than 1,000 and having at least one polymerizableunsaturated group per molecule, and

(c) 1 to 100 parts by weight, relative to 100 parts by weight of theresin (a), of an inorganic porous material.

For easy understanding of the present invention, the essential featuresand various embodiments of the present invention are enumerated below.

-   1. A photosensitive resin composition for forming a laser engravable    printing element, comprising:

(a) 100 parts by weight of a resin which is a plastomer at 20° C.,wherein the resin has a number average molecular weight of from 1,000 to100,000 and has a polymerizable unsaturated group in an amount such thatthe average number of the polymerizable unsaturated group per moleculeis at least 0.7,

(b) 5 to 200 parts by weight, relative to 100 parts by weight of theresin (a), of an organic compound having a number average molecularweight of less than 1,000 and having at least one polymerizableunsaturated group per molecule, and

(c) 1 to 100 parts by weight, relative to 100 parts by weight of theresin (a), of an inorganic porous material.

-   2. The photosensitive resin composition according to item 1 above,    wherein the inorganic porous material (c) has a number average    particle diameter of from 0.1 μm to 100 μm, an average pore diameter    of from 1 nm to 1,000 nm, and a pore volume of from 0.1 ml/g to 10    ml/g.-   3. The photosensitive resin composition according to item 1 or 2    above, wherein the resin composition further comprises (d) a    photopolymerization initiator.-   4. The photosensitive resin composition according to any one of    items 1 to 3 above, wherein at least 20% by weight of the organic    compound (b) is a compound having at least one functional group    selected from the group consisting of an alicyclic functional group    and an aromatic functional group.-   5. The photosensitive resin composition according to any one of    items 1 to 4 above, wherein the inorganic porous material (c) has a    specific surface area of from 10 m²/g to 1,500 m²/g, and exhibits an    oil absorption of from 10 ml/100 g to 2,000 ml/100 g.-   6. The photosensitive resin composition according to any one of    items 1 to 5 above for use in forming a relief printing element.-   7. A laser engravable printing element which is a cured    photosensitive resin composition having a shape of a sheet or    cylinder, wherein the laser engravable printing element contains an    inorganic porous material.-   8. A multi-layered, laser engravable printing element comprising a    printing element layer and at least one elastomer layer provided    below the printing element layer, wherein the printing element layer    is made of the laser engravable printing element of item 7 above and    the elastomer layer has a Shore A hardness of from 20 to 70.-   9. The multi-layered, laser engravable printing element according to    item 8 above, wherein the elastomer layer is produced by photocuring    a resin which is in a liquid state at room temperature.-   10. A laser engravable printing element obtainable by a process    comprising:

shaping the photosensitive resin composition according to any one ofitems 1 to 6 above into a sheet or cylinder, and

crosslink-curing the photosensitive resin composition by light orelectron beam irradiation.

-   11. A multi-layered, laser engravable printing element comprising a    printing element layer and at least one elastomer layer provided    below the printing element layer, wherein the printing element layer    is made of the laser engravable printing element of item 10 above    and the elastomer layer has a Shore A hardness of from 20 to 70.-   12. The multi-layered, laser engravable printing element according    to item 11 above, wherein the elastomer layer is produced by    photocuring a resin which is in a liquid state at room temperature.-   13. A laser engravable printing element obtained by a process    comprising:

shaping the photosensitive resin composition according to any one ofitems 1 to 6 above into a sheet or cylinder, and

crosslink-curing the photosensitive resin composition by light orelectron beam irradiation.

-   14. A multi-layered, laser engravable printing element comprising a    printing element layer and at least one elastomer layer provided    below the printing element layer, wherein the printing element layer    is made of the laser engravable printing element of item 13 above    and the elastomer layer has a Shore A hardness of from 20 to 70.-   15. The multi-layered, laser engravable printing element according    to item 14 above, wherein the elastomer layer is produced by    photocuring a resin which is in a liquid state at room temperature.

Hereinbelow, the present invention is explained in more detail.

The photosensitive resin composition of the present invention comprises(a) 100 parts by weight of a resin which is a plastomer at 20° C.,wherein the resin has a number average molecular weight of from 1,000 to100,000 and has a polymerizable unsaturated group in an amount such thatthe average number of the polymerizable unsaturated group per moleculeis at least 0.7, (b) 5 to 200 parts by weight, relative to 100 parts byweight of resin (a), of an organic compound having a number averagemolecular weight of less than 1,000 and having at least onepolymerizable unsaturated group per molecule, and (c) 1 to 100 parts byweight, relative to 100 parts by weight of resin (a), of an inorganicporous material. In the present invention, the term “laser engravableprinting element” means a cured resin material which is used as a basematerial of a printing plate, namely a cured resin material prior to thelaser engraving.

The photosensitive resin composition of the present invention is aplastomer at 20° C. because resin (a), which is the main component ofthe resin composition, is a plastomer. In the present invention, theterm “plastomer” means, as defined in “Shinpan Koubunshi Jiten (PolymerDictionary, New Edition” edited by Society of Polymer Science Japan(published in 1988 by Asakura Shoten, Japan), a polymer which has theability to be relatively easily deformed, or the ability to be easilyflowed by heating and be solidified upon cooling. This “plastomer” is aterm which is against the term “elastomer” (which means a materialhaving the ability to change a shape thereof in accordance with a forceapplied thereto and to recover the original shape thereof within a shortperiod of time after released from the force).

The viscosity of the photosensitive resin composition of the presentinvention at 20° C. is preferably from 10 Pa·s to 10 kPa·s, morepreferably from 50 Pa·s to 5 kPa·s. When the viscosity of the resincomposition is in the above-mentioned range, such a resin compositioncan be easily shaped into a sheet or cylinder, and the shaping processcan be performed with ease. On the other hand, when the viscosity of theresin composition is less than 10 Pa·s, the ability of the inorganicporous material to absorb the debris becomes unsatisfactory. The reasonfor this has not yet been elucidated, but it is considered that a lowviscosity photosensitive resin composition is likely to enter themicropores and voids of the inorganic porous material, to thereby fillup many of the micropores and voids, thus preventing the inorganicporous material from absorbing the debris. Further, when a printingelement is produced from a resin composition having a viscosity of lessthan 10 Pa·s, the mechanical strength of the printing element becomesunsatisfactory. In addition, shaping of the resin composition into acylindrical printing element becomes difficult and, even when acylindrical printing element is obtained, the preservation of thecylindrical shape of the printing element becomes difficult. On theother hand, when the viscosity of the resin composition exceeds 10kPa·s, shaping of such a resin composition and processing of the shapedarticle become difficult at room temperature. In the present invention,as mentioned above, the resin composition is a plastomer and, hence, arelief printing element (in the form of a sheet or cylinder) formed fromthe resin composition has high uniformity in thickness and highdimensional precision.

With respect to resin (a) used for producing the photosensitive resincomposition of the present invention, there is no particular limitationso long as the resin is a plastomer at 20° C., has a number averagemolecular weight of from 1,000 to 100,000 and has a polymerizableunsaturated group in an amount such that the average number of thepolymerizable unsaturated group per molecule is at least 0.7.

The number average molecular weight of resin (a) is in the range of from1,000 to 100,000, preferably from 2,000 to 100,000, more preferably from5,000 to 100,000. When a resin composition is produced using resin (a)having a number average molecular weight in the above-mentioned range,such a resin composition exhibits excellent processability. Further, aprinting element obtained by crosslink-curing such a resin compositionexhibits high strength, and a relief structure formed from the printingelement also exhibits high strength and endures repeated use. On theother hand, when a resin composition is produced using resin (a) havinga number average molecular weight of less than 1,000, the strength ofthe printing element produced from such a resin composition becomesunsatisfactory. Further, when a resin composition is produced usingresin (a) having a number average molecular weight of more than 100,000,the viscosity of such a resin composition becomes too high and acomplicated processing method, such as heat extrusion, becomes necessaryfor producing a laser engravable printing element having a shape of asheet or cylinder. The number average molecular weight of resin (a) isdetermined by GPC (gel permeation chromatography) in which a calibrationcurve prepared using standard polystyrene samples is employed.

Further, resin (a) has a polymerizable unsaturated group in an amountsuch that the average number of the polymerizable unsaturated group permolecule is at least 0.7. In the present invention, the “polymerizableunsaturated group” means a polymerizable unsaturated group whichparticipates in a radical or addition polymerization reaction. Preferredexamples of polymerizable unsaturated groups which participate in aradical polymerization reaction include a vinyl group, an acetylenegroup, an acryl group, a methacryl group and an allyl group. Preferredexamples of polymerizable unsaturated groups which participate in anaddition polymerization reaction include a cinnamoyl group, a thiolgroup, an azido group, an epoxy group which participates in aring-opening addition reaction, an oxetane group, a cyclic ester group,a dioxysilane group, a spiro-o-carbonate group, a spiro-o-ester group, abicyclo-o-ester group, a cyclohexane group and a cyclic iminoethergroup.

The polymerizable unsaturated group present in the molecule of resin (a)may be an unsaturated group which is bonded directly to the terminal ofa main chain or side chain of resin (a), or to the non-terminal portionof the main chain or side chain of resin (a). By the use of resin (a)which has a polymerizable unsaturated group in an amount such that theaverage number of the polymerizable unsaturated group per molecule is atleast 0.7, a printing element formed from the resin composition of thepresent invention exhibits excellent mechanical strength and the reliefstructure formed on the printing element is unlikely to sufferdistortion during the laser engraving. Further, the relief structureexhibits excellent durability and endures repeated use. From theviewpoint of obtaining a printing element having excellent mechanicalstrength, it is preferred that resin (a) has the polymerizableunsaturated group in an amount such that the average number of thepolymerizable unsaturated group per molecule of resin (a) is morethan 1. The increase in the average number of the polymerizableunsaturated group per molecule of resin (a) leads to an improvement inthe solvent resistance and mechanical strength of the resin composition.When a resin (a) molecule has polymerizable unsaturated groups only atthe terminals thereof, the number of the polymerizable unsaturatedgroups contained in the resin (a) molecule is 2, but when the resin (a)molecule has a branched structure in which the polymerizable functionalgroup(s) is/are bonded to side chain(s), the number of the polymerizableunsaturated groups contained in the resin (a) molecule becomes more than2. Therefore, it is impossible to limit the maximum number of thepolymerizable unsaturated groups contained in a resin (a) molecule, butit is considered to be about 20. The average number of the polymerizableunsaturated group per molecule of resin (a) is determined by themolecular structure analysis of resin (a), which is performed by NMR(nuclear magnetic resonance spectroscopy). Specifically, in the presentinvention, ¹H (proton) NMR is used for the analysis. ¹³C-NMR can be usedin combination with the proton NMR. In the case of the proton NMR, fromthe viewpoint of achieving excellent resolution in the NMR spectrum, itis preferred that the detection frequency of the NMR apparatus is 100MHz or more.

Specific examples of resins which can be used in resin (a) includepolymers in which component monomer units are bonded throughcarbon-carbon linkages, such as polyolefins (e.g., a polyethylene and apolypropylene), polydienes (e.g., a polybutadiene and a polyisoprene),polyhaloolefins (e.g., a polyvinyl chloride and a polyvinilidenechloride), a polystyrene, a polyacrylonitrile, a polyvinyl alcohol, apolyvinyl acetate, a polyvinyl acetal, a polyacrylic acid, apoly(meth)acrylate, a poly(meth)acrylamide and a polyvinyl ether;polyethers, such as a polyphenylene ether; and polymers comprising aheteroatom in the main chain thereof, such as a polyethyleneterephthalate, a polycarbonate, a polyacetal, a polyurethane, a nylon, apolyurea and a polyimide. One or more polymers can be used in resin (a).When a plurality of different polymers is used in combination, thepolymers may be in the form of either a copolymer or a polymer blend.

Especially when it is intended to obtain a resin composition which canbe used for forming a flexible relief pattern, such as the reliefpattern of a flexographic printing plate, it is preferred that at leasta part of resin (a) is a plastomer having a glass transition temperatureof 20° C or less, more preferably 0° C. or less. Examples of suchplastomers include hydrocarbon polymers, such as a polyethylene, apolybutadiene, a hydrogenated polybutadiene, a polyisoprene and ahydrogenated polyisoprene; polyesters, such as a polyadipate and apolycaprolactone; polyethers, such as a polyethylene glycol, apolypropylene glycol and a polytetramethylene glycol; aliphaticpolycarbonates; silicones, such as a polydimethylsiloxane; polymers ofacrylic acid, (meth)acrylic acid and/or derivatives thereof; andmixtures and copolymers thereof. It is preferred that theabove-mentioned plastomer having a low glass transition temperature isused in an amount of from 30 to 100% by weight, based on the totalweight of the resins used as resin (a).

When it is intended to emboss the photosensitive resin composition ofthe present invention, it is preferred that resin (a) is a rigid resin,such as a polyurethane or a polyimide.

With respect to the method for obtaining resin (a), for example, therecan be mentioned a method in which a polymerizable unsaturated group isdirectly introduced to the terminals of a polymer (e.g., any of theabove-mentioned polymers which can be used in resin (a)). As anotherexample of the method for obtaining resin (a), there can be mentionedthe following method. A reactive polymer is produced by introducing aplurality of reactive groups (such as a hydroxyl group, an amino group,an epoxy group, a carboxyl group, an acid anhydride group, a ketonegroup, a hydrazine group, an isocyanate group, an isothiocyanate group,a cyclic carbonate group and an ester group) into a polymer (e.g., anyof the above-mentioned polymers which can be used in resin (a)) whichhas a molecular weight of several thousands. The produced reactivepolymer is reacted with a binding compound capable of binding to thereactive groups of the polymer (for example, when the reactive group ofthe polymer is a hydroxyl group or an amino group, a polyisocyanate canbe used as the binding compound), to thereby adjust the molecular weightof the polymer and convert the terminals of the polymer into bindinggroups. Subsequently, an organic compound having a polymerizableunsaturated group as well as a group which is capable of reacting withthe terminal binding groups of the reactive polymer is reacted with thereactive polymer to introduce the polymerizable unsaturated group intothe terminals of the reactive polymer, thereby obtaining resin (a).

Organic compound (b) used for producing the photosensitive resincomposition of the present invention is an organic compound having anumber average molecular weight of less than 1,000 and having at leastone polymerizable unsaturated group per molecule. From the viewpoint ofease in blending organic compound (b) with resin (a), the number averagemolecular weight of the organic compound (b) must be less than 1,000.With respect to the design of a photosensitive resin composition, ingeneral, the combination of a compound having a relatively highmolecular weight and a compound having a relatively low molecular weightis effective for producing a resin composition which exhibits excellentmechanical properties after being cured. When a photosensitive resincomposition is produced using only compounds having relatively lowmolecular weights, such a resin composition is disadvantageous not onlyin that the resin composition suffers a marked cure shrinkage at thetime of photocuring, but also in that a long time is needed for thecuring the resin composition. On the other hand, when a photosensitiveresin composition is produced using only compounds having relativelyhigh molecular weights, it becomes difficult to cure such a resincomposition and obtain a cured resin having excellent properties.Therefore, in the present invention, resin (a) having a high molecularweight and organic compound (b) having a low molecular weight are usedin combination.

The number average molecular weight of the organic compound (b) isdetermined as follows. When the ratio of the weight average molecularweight Mw to the number average molecular weight Mn (i.e., thepolydispersity Mw/Mn), which are determined by GPC, is 1.1 or more, thenumber average molecular weight is defined as the Mn value determined byGPC. When the polydispersity is 1.0 or more and less than 1.1 and only asingle peak is observed in the gel permeation chromatogram, themolecular weight distribution of the organic compound (b) is very small.In such a case, the number average molecular weight is determined byGPC-MS (a method in which a mass spectroscopy is performed with respectto each component separated by gel permeation chromatography). When thepolydispersity is less than 1.1 and a plurality of peaks are observed inthe gel permeation chromatogram (i.e., when the organic compound (b) isa mixture of a plurality of different compounds (b) having differentmolecular weights), the weight ratio of the different compounds (b) iscalculated from the area ratio of the peaks observed in the gelpermeation chromatogram, and the number average molecular weight of theorganic compound (b) is determined using the weight ratio of thedifferent compounds (b).

As in the case of the “polymerizable unsaturated group” of resin (a)which is explained above, the “polymerizable unsaturated group” oforganic compound (b) means a polymerizable unsaturated group whichparticipates in a radical or addition polymerization reaction. Preferredexamples of polymerizable unsaturated groups which participate in aradical polymerization reaction include a vinyl group, an acetylenegroup, an acryl group, a methacryl group and an allyl group. Preferredexamples of polymerizable unsaturated groups which participate in anaddition polymerization reaction include a cinnamoyl group, a thiolgroup, an azido group, an epoxy group which participates in aring-opening addition reaction, an oxetane group, a cyclic ester group,a dioxysilane group, a spiro-o-carbonate group, a spiro-o-ester group, abicyclo-o-ester group, a cyclohexane group and a cyclic iminoethergroup. There is no particular limitation with respect to the number ofpolymerizable unsaturated groups of organic compound (b) so long as theorganic compound (b) has at least one polymerizable unsaturated groupper molecule. It is impossible to limit the maximum number of thepolymerizable unsaturated group per molecule for the same reason asmentioned above in connection with resin (a), but it is considered to beabout 10. As in the case of resin (a), in the present invention, thenumber of the polymerizable unsaturated group per molecule of theorganic compound (b) is a value determined by ¹H-NMR.

Specific examples of organic compound (b) include olefins, such asethylene, propylene, styrene and divinylbenzene; acetylene typecompounds; (meth)acrylic acid and derivatives thereof; haloolefins;unsaturated nitriles, such as acrylonitrile; (meth)acrylamide andderivatives thereof; allyl compounds, such as an allyl alcohol and anallyl isocyanate; unsaturated dicarboxylic acids (such as maleicanhydride, maleic acid and fumaric acid) and derivatives thereof; vinylacetate; N-vinylpyrrolidone; and N-vinylcarbazole. From the viewpoint ofvarious advantages, such as availability of various types of products,reasonable price and decomposability by laser beam irradiation,(meth)acrylic acid and derivatives thereof are preferred. Theabove-mentioned compounds (b) can be used individually or in combinationdepending on the use of the photosensitive resin composition.

Examples of derivatives of the compounds mentioned above as compound (b)include compounds having an alicyclic group, such as a cycloalkyl group,a bicycloalkyl group, a cycloalkylene group or a bicycloalkylene group;compounds having an aromatic group, such as a benzyl group, a phenylgroup, a phenoxy group or a fluorenyl group; compounds having a group,such as an alkyl group, a halogenated alkyl group, an alkoxyalkyl group,a hydroxyalkyl group, an aminoalkyl group, a tetrahydrofurfuryl group,an allyl group or a glycidyl group; esters with a polyol, such as analkylene glycol, a polyoxyalkylene glycol, an(alkyl/allyloxy)polyalkylene glycol or trimethylol propane. Organiccompound (b) can be a heterocyclic type aromatic compound containingnitrogen, sulfur or the like as a heteroatom. For example, since theprinting element formed by the photosensitive resin composition of thepresent invention is used for forming a printing plate, for suppressingthe swelling of the printing plate by a solvent for the printing ink(i.e., an organic solvent, such as an alcohol or an ester), it ispreferred that organic compound (b) is a compound having a long chainaliphatic group, an alicyclic group or an aromatic group.

Further, especially when it is intended to use the resin composition ofthe present invention in the field where the resin composition isrequired to have high rigidity, it is preferred that organic compound(b) is a compound having an epoxy group which participates in aring-opening addition reaction. As compounds having an epoxy group whichparticipates in a ring-opening addition reaction, there can be mentionedcompounds which are obtained by reacting epichlorohydrin with any ofvarious polyols (such as diols and triols); and epoxy compounds obtainedby reacting a peracid with an ethylenic bond in an ethylenicbond-containing compound. Specific examples of such compounds includeethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether,triethylene glycol diglycidyl ether, tetraethylene glycol diglycidylether, polyethylene glycol diglycidyl ether, propylene glycol diglycidylether, tripropylene glycol diglycidyl ether, polypropylene glycoldiglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanedioldiglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether,trimethylol propane triglycidyl ether, bisphenol A diglycidyl ether,hydrogenated bisphenol A diglycidyl ether, diglycidyl ethers of acompound formed by addition-bonding ethylene oxide or propylene oxide tobisphenol A, polytetramethylene glycol diglycidyl ether, poly(propyleneglycol adipate)diol diglycidyl ether, poly(ethylene glycol adipate)dioldiglycidyl ether, poly(caprolactone)diol diglycidyl ether,3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexylcarboxylate,1-methyl-3,4-epoxycyclohexylmethyl1′-methyl-3′,4′-epoxycyclohexylcarboxylate,bis[1-methyl-3,4-epoxycyclohexyl] adipate, vinylcyclohexene diepoxide,polyepoxy compounds (each independently obtained by reacting a peraceticacid with a polydiene (such as polybutadiene or polyisoprene)), andepoxidized soybean oil.

In the present invention, it is preferred that at least 20% by weight,more preferably 50 to 100% by weight of organic compound (b) is acompound having at least one functional group selected from the groupconsisting of an alicyclic functional group and an aromatic functionalgroup. The mechanical strength and solvent resistance of thephotosensitive resin composition can be improved by the use of organiccompound (b) having an alicyclic functional group and/or an aromaticfunctional group. Examples of alicyclic functional groups contained inthe organic compound (b) include a cycloalkyl group, a bicycloalkylgroup, a cycloalkene skeleton and a bicycloalkene skeleton, and examplesof organic compounds (b) having an alicyclic group include cyclohexylmethacrylate. Examples of aromatic functional groups contained in theorganic compound (b) include a benzyl group, a phenyl group, a phenoxygroup and a fluorene group, and examples of organic compounds (b) havingan aromatic group include benzyl methacrylate and phenoxyethylmethacrylate. Organic compound (b) containing an aromatic functionalgroup can be a heterocyclic type aromatic compound containing nitrogen,sulfur and the like as a heteroatom.

For improving the impact resilience of a printing plate obtained fromthe photosensitive resin composition of the present invention, the typeof the organic compound (b) can be appropriately selected, based on theconventional knowledge on photosensitive resin compositions for formingprinting plates (for example, a methacyrlic monomer described inUnexamined Japanese Patent Application Laid-Open Specification No. Hei7-239548 can be used).

The photosensitive resin composition of the present invention comprisesinorganic porous material (c). Inorganic porous material (c) isinorganic microparticles having micropores and/or very small voids. Inthe present invention, a photosensitive resin having a relatively lowmolecular weight is used to produce the photosensitive resin compositionso as to enable an easy engraving with laser beam; therefore, when thepolymer chains of the photosensitive resin are broken by laser beam,viscous liquid debris composed of low molecular weight components (i.e.,monomers and oligomers) are generated in a large amount. In the presentinvention, inorganic porous material (c) is used to conduct anabsorption removal of the generated liquid debris. Further, the presenceof inorganic porous material (c) prevents the occurrence of surface tackof the printing plate. The removal of liquid debris by the inorganicporous material is a completely new technique which has notconventionally been known. The photosensitive resin composition of thepresent invention which is capable of quickly removing the liquid debrisis especially advantageous for the formation of a flexographic printingplate, which formation is accompanied by a generation of a large amountof engraving debris.

In the present invention, as mentioned above, inorganic microparticlesare used as inorganic porous material (c). The inorganic microparticlesare used because they are not molten or deformed by laser beamirradiation and maintain their pores and/or small voids. Therefore, withrespect to the material of the inorganic porous material (c), there isno particular limitation so long as the material is not molten by laserbeam irradiation. However, when it is intended to photocure thephotosensitive resin composition of the present invention by ultravioletlight or visible light, the use of black microparticles as inorganicporous material (c) is unfavorable since the black particles cause amarked lowering of the transmission of light to the inner portion of theresin composition, thereby lowering the properties of the cured resincomposition. Thus, black microparticles, such as carbon black, activatedcarbon and graphite, are not suitable as inorganic porous material (c)used in the resin composition of the present invention.

The characteristics and properties of inorganic porous material (c),such as a number average particle diameter, a specific surface area, anaverage pore diameter, a pore volume, an ignition loss and an oilabsorption, are very important factors for achieving an efficientremoval of viscous liquid debris. Among the conventional microparticleswhich are used as additives for a photosensitive resin composition,there are nonporous microparticles and porous microparticles having toosmall pores which are incapable of satisfactorily absorbing the liquiddebris. In addition to the above-mentioned characteristics andproperties of inorganic porous material (c), the molecular weight andviscosity of the photosensitive resin also have a great influence on theefficiency of the removal of the viscous liquid debris. It is preferredthat the porous material which is used as inorganic porous material (c)in the present invention has a number average particle diameter of from0.1 μm to 100 μm, an average pore diameter of from 1 nm to 1,000 nm, anda pore volume of from 0.1 ml/g to 10 ml/g.

In the present invention, the number average particle diameter of theinorganic porous material (c) is preferably in the range of from 0.1 μmto 100 μm, more preferably from 0.5 to 20 μm, most preferably from 3 to10 μn. When a porous material having a number average particle diameterof less than 0.1 μm is used in the photosensitive resin composition,dust arises during the laser engraving of the printing element formedfrom the photosensitive resin composition, thereby staining theengraving apparatus with the dust. Further, when such an inorganicporous material is mixed with resin (a) and organic compound (b),problems are likely to arise, such as an increase in the viscosity ofthe resultant mixture, an incorporation of air bubbles into the mixture,and a generation of dust. On the other hand, when a porous materialhaving a number average particle diameter of more than 100 μm is used toproduce a photosensitive resin composition, disadvantages are likely tobe caused wherein the relief pattern formed on the printing element bylaser engraving is chipped, so that an image of a print obtained usingthe relief pattern becomes imprecise. In the present invention, theaverage pore diameter is determined by means of a laser scatteringparticle size distribution analyzer.

The average pore diameter of inorganic porous material (c) has a greatinfluence on the ability thereof to absorb the liquid debris which isgenerated during the laser engraving. The average pore diameter ispreferably in the range of from 1 nm to 1,000 nm, more preferably from 2nm to 200 nm, still more preferably from 2 nm to 50 nm. When the averagepore diameter of an inorganic porous material is less than 1 nm, such aninorganic porous material is incapable of absorbing a satisfactoryamount of the liquid debris generated during the laser engraving. On theother hand, when the average pore diameter of an inorganic porousmaterial exceeds 1,000 nm, the specific surface area of such aninorganic porous material becomes too small to absorb a satisfactoryamount of the liquid debris. The reason why an inorganic porous materialhaving an average pore diameter of less than 1 nm cannot absorb asatisfactory amount of the liquid debris is not fully elucidated, but itis considered that the viscous liquid debris is difficult to enter intothe micropores having such a small average pore diameter. For example, azeolite, a mordenite, a hollandite, a todorokite and a faujasite areporous materials having micropores of less than 1 nm. Each of theseporous material has a large specific surface area; however, theirability to remove the liquid debris is low. Among various porousmaterials, those which have an average pore diameter of from 2 to 50 nmare called “mesoporous materials”. Such mesoporous materials areespecially preferred in the present invention because the mesoporousmaterials have remarkably high ability to absorb the liquid debris. Inthe present invention, the average pore diameter is determined by thenitrogen adsorption method. In addition, the pore diameter distributioncan also be determined by the nitrogen adsorption method using anitrogen adsorption isotherm obtained at −196° C.

The pore volume of inorganic porous material (c) is preferably in therange of from 0.1 ml/g to 10 ml/g, more preferably from 0.2 ml/g to 5ml/g. When the pore volume of an inorganic porous material is less than0.1 ml/g, such an inorganic porous material is incapable of absorbing asatisfactory amount of the liquid debris generated during the laserengraving. On the other hand, when the pore volume exceeds 10 ml/g, themechanical properties of the particles become unsatisfactory. In thepresent invention, the pore volume is a value determined by the nitrogenadsorption method. Specifically, the pore volume is determined from anitrogen adsorption isotherm obtained at −196° C.

In order to evaluate the porous structure of a porous material, thepresent inventors have adopted a new parameter called “specificporosity”. The “specific porosity” of porous particles is the ratio ofthe specific surface area (P) of the particles to the surface area (S)per unit weight of the particles, namely P/S, wherein S is a valuecalculated from the average pore diameter (D) (unit: μm) of theparticles and the density (d) (unit: g/cm³) of a substance constitutingthe particles. With respect to the surface area (S) per unit weight ofthe porous particles, when the particles are spherical, the averagesurface area of the particles is πD²×10⁻¹² (unit: m²) and the averageweight of the particles is (πD³ d/6)×10⁻¹² (unit: g). Accordingly, thesurface area (S) per unit weight of the particles is calculated by thefollowing formula:S=6/(Dd) (unit: m²/g)When the porous particles are not spherical, certain particles arechosen, and the surface area (S) per unit weight of the particles iscalculated on the assumption that the chosen particles are sphereswherein the maximum axes of the chosen particles are defined as thediameters of the spheres.

The specific surface area (P) is a value calculated from the amount ofmolecular nitrogen adsorbed on the surface of a particle.

The specific surface area P increases as the particle diameter decreasesand, therefore, the specific surface area alone is inappropriate as aparameter for defining the porous structure of a porous material.Therefore, the present inventors have adopted the above-mentioned“specific porosity” as a nondimensional parameter, taking intoconsideration the particle diameter of the porous material. It ispreferred that the inorganic porous material (c) used in the presentinvention has a specific porosity of 20 or more, more advantageously 50or more, most advantageously 100 or more. When the specific porosity ofthe inorganic porous material (c) is 20 or more, the inorganic porousmaterial (c) is effective for the absorption removal of the liquiddebris.

For example, carbon black, which is conventionally widely used as areinforcing agent for a rubber and the like, has a very large specificsurface area, namely 150 m²/g to 20 m²/g, and has a very small averageparticle diameter, generally 10 nm to 100 nm. Since it is known thatcarbon black generally has a graphite structure, the specific porosityof carbon black can be calculated using the density of graphite, i.e.,2.25 g/cm³. The specific porosity of carbon black obtained by suchcalculation is in the range of from 0.8 to 1.0, which indicates thatcarbon black is a non-porous material. On the other hand, the poroussilica used in the Examples of the present application have a specificporosity which is much larger than 500.

Further, for achieving excellent absorption, it is preferred thatinorganic porous material (c) has a specific surface area of from 10m²/g to 1,500 m²/g, and exhibits an oil absorption of from 10 ml/100 gto 2,000 ml/100 g.

The specific surface area of inorganic porous material (c) is preferablyin the range of from 10 M²/g to 1,500 m²/g, more preferably from 100m²/g to 800 m²/g. When the specific surface area of an inorganic porousmaterial is less than 10 m²/g, the ability thereof to remove the liquiddebris generated during laser engraving is likely to becomeunsatisfactory. On the other hand, when the specific surface area of aninorganic porous material exceeds 1,500 m²/g, a disadvantage is likelyto be caused that the viscosity of the photosensitive resin compositioncontaining the inorganic porous material is increased and the thixotropyof the photosensitive resin composition is increased. In the presentinvention, the specific surface area is determined by the BET methodusing the nitrogen adsorption isotherm obtained at −196° C.

The oil absorption of inorganic porous material (c) is an index forevaluating the amount of liquid debris which the inorganic porousmaterial can absorb, and it is defined as an amount of oil absorbed by100 g of the inorganic porous material. The oil absorption of theinorganic porous material (c) used in the present invention ispreferably in the range of from 10 ml/100 g to 2,000 ml/100 g, morepreferably from 50 ml/100 g to 1,000 ml/100 g. When the oil absorptionof an inorganic porous material is less than 10 ml/100 g, it is likelythat such an inorganic porous material cannot effectively remove theliquid debris generated by laser engraving. On the other hand, when theoil absorption of an inorganic porous material exceeds 2,000 ml/100 g,the mechanical properties of such an inorganic porous material arelikely to become unsatisfactory. The oil absorption is determined inaccordance with JIS-K5101.

Since the photosensitive resin composition of the present invention isused for forming a laser engravable printing element, inorganic porousmaterial (c) needs to maintain its porous structure without sufferingdeformation or melting by laser beam irradiation, especially infraredradiation. Therefore, it is desired that the ignition loss of inorganicporous material (c) at 950° C. for 2 hours is not more than 15% byweight, preferably not more than 10% by weight.

There is no particular limitation with respect to the shape of theparticles of inorganic porous material (c), and each particle ofinorganic porous material (c) may independently be in the form of asphere, a plate or a needle. Alternatively, inorganic porous material(c) may not have any definite shape or may be in the form of particleseach having a projection(s) on the surface thereof. Further, inorganicporous material (c) may be hollow particles or spherical granules, suchas silica sponge, which have uniform pore diameter. Specific examples ofinorganic porous material (c) include a porous silica, a mesoporoussilica, a silica-zirconia porous gel, a mesoporous molecular sieve, aporous alumina and a porous glass.

In addition, a lamellar substance, such as a lamellar clay compound,having voids between the layers can be also used as inorganic porousmaterial (c), wherein the size of each void (distance between thelayers) ranges from several to 100 nm. In such a lamellar substance, thevoid between the layers thereof (i.e., the space between the layers) isdefined as a pore, and the total amount of the spaces between themutually adjacent layers is defined as a pore volume. These values canbe obtained from the nitrogen adsorption isotherm.

In the present invention, the substances exemplified above as inorganicporous material (c) can be used individually or in combination.

In general, carbon black which has conventionally been used as anadditive for a photosensitive resin is considered to have a graphitestructure, namely a lamellar structure. In the graphite, each intervalbetween the layers is very small, namely 0.34 nm, so that the absorptionof viscous liquid debris by carbon black is difficult. In addition,since the color of carbon black is black, it exhibits strong lightabsorbing properties with respect to wide range of wavelengths (rangingfrom UV light to infrared light). Therefore, when carbon black is addedto a photosensitive resin composition and the resultant resincomposition is photocured with UV light and the like, it becomesnecessary to limit the amount of carbon black to a very small amount.Accordingly, carbon black is not suitable as inorganic porous material(c) which is used for the absorption removal of viscous liquid debris.

In the present invention, inorganic porous material (c) havingincorporated in its pores and/or voids an organic colorant (such as apigment or a dye) which is capable of absorbing light having anwavelength of a laser beam can be used.

In addition, the surface of the inorganic porous material may bemodified by coating the surface with a silane coupling agent, a titaniumcoupling agent or an organic compound, to thereby obtain particleshaving an improved hydrophilic or hydrophobic property.

The amounts of resin (a), organic compound (b) and inorganic porousmaterial (c) used in the photosensitive resin composition of the presentinvention are as follows. In general, the amount of organic compound (b)is 5 to 200 parts by weight, preferably 20 to 100 parts by weight,relative to 100 parts by weight of resin (a). The amount of inorganicporous material (c) is 1 to 100 parts by weight, preferably 1 to 50parts by weight, more preferably 2 to 35 parts by weight, still morepreferably 2 to 20 parts by weight, most preferably 2 to 15 parts byweight, relative to 100 parts by weight of resin (a).

When the amount of organic compound (b) is less than 5 parts by weight,a printing plate or the like which is obtained from the photosensitiveresin composition is likely to suffer disadvantages, such as adifficulty in maintaining a good balance between the rigidity of thecomposition, and the tensile strength and elongation of the composition.When the amount of organic compound (b) exceeds 200 parts by weight, thephotosensitive resin composition is likely to suffer not only a markedcure shrinkage at the time of the crosslink-curing of the resincomposition, but also a lowering of the uniformity in thickness of theresultant printing element.

When the amount of inorganic porous material (c) is less than 1 part byweight, depending on the types of resin (a) and organic compound (b)used, the abilities of the inorganic porous material to prevent surfacetack and to remove the liquid debris generated by laser engraving becomeunsatisfactory. On the other hand, when the amount of inorganic porousmaterial (c) exceeds 100 parts by weight, a printing plate which isobtained from the photosensitive resin composition becomes fragile andloses transparency. Especially when a flexographic printing plate isproduced using a resin composition containing too large an amount ofinorganic porous material (c), the rigidity of such a flexographicprinting plate may become too high.

When a laser engravable printing element is formed by photocuring aphotosensitive resin composition (especially when the photocuring isperformed using an UV light), the light transmittance of the resincomposition influences the curing reaction. Therefore, as inorganicporous material (c), it is advantageous to use an inorganic porousmaterial having a refractive index which is similar to that of thephotosensitive resin composition.

In the production of the laser engravable printing element from thephotosensitive resin composition of the present invention, thephotosensitive resin composition is crosslink-cured by irradiationthereof with light or electron beam. For promoting the crosslink-curingof the photosensitive resin composition, it is preferred that thephotosensitive resin composition further comprises photopolymerizationinitiator (d). Photopolymerization initiator (d) can be appropriatelyselected from those which are customarily used. Examples ofpolymerization initiators usable as component (d) include a radicalpolymerization initiator, a cationic polymerization initiator and ananionic polymerization initiator which are exemplified in “KoubunshiDeta Handobukku—Kisohen (Polymer Data Handbook—Fundamentals)” edited byPolymer Society Japan, published in 1986 by Baifukan Co., Ltd., Japan.In the present invention, the crosslink-curing of the photosensitiveresin composition which is performed by photopolymerization using aphotopolymerization initiator is advantageous for improving theproductivity of the printing element while maintaining the storagestability of the resin composition. Representative examples ofconventional photopolymerization initiators which can be used asphotopolymerization initiator (d) include benzoin; benzoin alkyl ethers,such as benzoin ethyl ether; acetophenones, such as2-hydroxy-2-methyl-propiophenone,4′-isopropyl-2-hydroxy-2-methylpropio-phenone,2,2-dimethoxy-2-phenylacetophenone and di-ethoxyacetophenone;photoradical initiators, such as 1-hydroxycyclohexyl phenyl ketone,2-methyl-1-[4-(methyl-thio)phenyl]-2-morpholino-propane-1-one, methylphenyl-glyoxylate, benzophenone, benzil, diacetyl, diphenyl-sulfide,eosin, thionine and anthraquinone; photo-cationic polymerizationinitiators, such as aromatic diazonium salt, an aromatic iodonium saltand an aromatic sulfonium salt, each of which generates an acid byabsorbing light; and photopolymerization initiators, each of whichgenerates a base by absorbing light. Photopolymerization initiator (d)is preferably used in an amount of from 0.01 to 10% by weight, based onthe total weight of resin (a) and organic compound (b).

In addition, depending on the use and desired properties of thephotosensitive resin composition, other additives, such as apolymerization inhibitor, an ultraviolet absorber, a dye, a pigment, alubricant, a surfactant, a plasticizer and a fragrance, may be added tothe photosensitive resin composition.

In another aspect of the present invention, there is provided a laserengravable printing element which is a cured photosensitive resincomposition having a shape of a sheet or cylinder, wherein the laserengravable printing element contains an inorganic porous material. It ispreferred that the laser engravable printing element of the presentinvention is a cured resin composition obtained by curing thephotosensitive resin composition of the present invention.

The laser engravable printing element of the present invention isobtained by photocuring a photosensitive resin composition whichcomprises an inorganic porous material. Therefore, when thephotosensitive resin composition of the present invention is used, athree-dimensionally crosslinked structure is formed by a reactionbetween the polymerizable unsaturated groups of resin (a) and thepolymerizable unsaturated groups of organic compound (b), and thecrosslinked resin composition becomes insoluble in the conventionallyused solvents, such as esters, ketones, aromatic compounds, ethers,alcohols and halogenated solvents. The crosslinking reaction involves areaction between resin (a) molecules, a reaction between organiccompound (b) molecules, and/or a reaction between a resin (a) moleculeand an organic compound (b) molecule, thus consuming the polymerizableunsaturated groups. With respect to the composition and structure of thelaser engravable printing element of the present invention, thedeterminations thereof can be conducted as follows. When the resincomposition is crosslink-cured using photopolymerization initiator (d),the photopolymerization initiator is decomposed with light. Theunreacted photopolymerization initiator and the decomposition productsthereof can be identified by extracting the crosslink-cured product witha solvent and analyzing the extracted product by GC-MS (a method inwhich products separated by gas chromatography are analyzed by massspectroscopy), LC-MS (a method in which products separated by liquidchromatography are analyzed by mass spectroscopy), GPC-MS (a method inwhich products separated by gel permeation chromatography are analyzedby mass spectroscopy), LC-NMR (a method in which products separated byliquid chromatography are analyzed by nuclear magnetic resonancespectroscopy). Further, by the analysis of the above-mentioned extractedproduct by GPC-MS, LC-NMR or GPC-NMR, it is also possible to identifythe unreacted resin (a), the unreacted organic compound (b) andrelatively low molecular weight products formed by the reaction betweenthe polymerizable unsaturated groups. With respect to a high molecularweight component which has a three-dimensionally crosslinked structureand is insoluble in a solvent, the thermal gravimetric GC-MS can be usedto detect the structures which have been formed by the reaction betweenthe polymerizable unsaturated groups and are present in the highmolecular weight component. For example, the presence of a structureformed by a reaction between the polymerizable unsaturated groups ofmethacrylate groups, acrylate groups, styrene monomers and the like canbe confirmed from the pattern of the mass spectrum. The thermalgravimetric GC-MS is a method in which a sample is decomposed by heat tothereby generate gas, and the generated gas is separated into componentsthereof by gas chromatography, followed by mass spectroscopic analysisof the separated components. When decomposed products derived from thephotopolymerization initiator and unreacted photopolymerizationinitiator are detected in the crosslink-cured product together with theunreacted polymerizable unsaturated groups or structures formed by areaction between the polymerizable unsaturated groups, it can beconcluded that the analyzed product is one obtained by photo-curing aphotosensitive resin composition.

The amount of the inorganic porous material contained in acrosslink-cured resin composition can be determined by heating acrosslink-cured resin composition in air, thereby burning the organiccomponents away from the resin composition, and measuring the weight ofthe residual product. Further, whether or not the residual product isthe inorganic porous material can be determined by observation of theshape of the residual product under a high resolution scanning electronmicroscope, measurement of the pore diameter distribution by means of alaser scattering particle size distribution analyzer, and measurementsof the pore volume, pore size distribution and specific surface area bythe nitrogen adsorption method.

The laser engravable printing element of the present invention ispreferably a laser engravable printing element which is obtainable by aprocess comprising:

shaping the photosensitive resin composition of the present inventioninto a sheet or cylinder, and

crosslink-curing the photosensitive resin composition by light orelectron beam irradiation. It is more preferred that the laserengravable printing element of the present invention is one obtained bythe above-mentioned process.

With respect to the method for shaping the photo-sensitive resincomposition of the present invention into a sheet or cylinder, any ofconventional methods employed for shaping resins can be employed. Forexample, there can be mentioned an injection molding method; a method inwhich a resin is extruded from a nozzle of a die by using a pump orextruder, followed by adjustment of the thickness of the extruded resinusing a blade; and a method in which a resin is subjected to calendarprocessing using a roll, thereby obtaining a resin sheet having adesired thickness. During the shaping of the resin composition, theresin composition can be heated at a temperature which does not causethe lowering of the properties of the resin. Further, if desired, theshaped resin composition may be subjected to a treatment using apressure roll or an abrasion treatment. In general, the resincomposition is shaped on an underlay called “back film” which is made ofPET (polyethylene terephthalate), nickel or the like. Alternatively, theresin composition can be shaped directly on a cylinder of a printingmachine. In this case, a seamless sleeve can be formed. Further, theshaping of the resin composition can be performed by means of asleeve-forming and engraving apparatus (which is an apparatus forcoating a liquid photosensitive resin composition on a cylinder andirradiating the coated photosensitive resin composition with light tothereby cure and solidify the resin composition, wherein the apparatusis also equipped with a laser source for laser engraving). When such anapparatus is used, the laser engraving can be performed immediatelyafter the formation of the sleeve, to thereby obtain a printing plate.Thus, a printing plate can be produced within an extremely short periodof time as compared to the case of the production of a printing plateusing a conventional rubber sleeve, where several weeks are needed.

The function of the above-mentioned “back film” is to impart dimensionalstability to the printing element. Therefore, it is preferred to use aback film having a high dimensional stability. Preferred examples ofmaterials for the back film include a metal, such as nickel, and amaterial having a coefficient of linear thermal expansion of not morethan 100 ppm/° C., more preferably not more than 70 ppm/° C. Specificexamples of materials for the back film include a polyester resin, apolyimide resin, a polyamide resin, a polyamideimide resin, apolyetherimide resin, a poly-bis-maleimide resin, a polysulfone resin, apolycarbonate resin, a polyphenylene ether resin, a polyphenylenethioether resin, a polyethersulfone resin, a liquid crystal resincomposed of a wholly aromatic polyester resin, a wholly aromaticpolyamide resin and an epoxy resin. Of these resins, a plurality ofdifferent resins may be used to produce a back film which is a laminateof layers of different resins. For example, a sheet formed by laminatinga 50 μm-thick polyethylene terephthalate sheet on each side of a 4.5μm-thick wholly aromatic polyamide film can be used. In addition, aporous sheet, such as a cloth obtained by weaving a fiber, a nonwovenfabric, or a porous film obtained by forming pores in a film, can bealso used as a back film. When a porous sheet is used as a back film,the pores of the porous film can be impregnated with a liquidphotosensitive resin composition, followed by photocuring of the resincomposition, to thereby unifying the cured resin layer with the backfilm and achieve a strong adhesion between the cured resin layer and theback film. Examples of fibers which can be used to form a cloth ornonwoven fabric include inorganic fibers, such as a glass fiber, analumina fiber, a carbon fiber, an alumina-silica fiber, a boron fiber, ahigh silicon fiber, a potassium titanate fiber and a sapphire fiber;natural fibers, such as cotton and linen; semisynthetic fibers, such asa rayon, an acetate and a promix; and synthetic fibers, such as a nylonfiber, a polyester fiber, an acryl fiber, a vinylon fiber, a polyvinylchloride fiber, a polyolefin fiber, a polyurethane fiber, a polyimidefiber and an aramid fiber. Cellulose produced by bacteria is a highlycrystalline nanofiber, and it can also be used to produce a thinnonwoven fabric having a high dimensional stability.

As a method for decreasing the coefficient of linear thermal expansionof the back film, there can be mentioned a method in which a filler isadded to the back film, and a method in which a meshed cloth of anaromatic polyamide, a glass cloth or the like is impregnated or coatedwith a resin. The fillers added to the back film can be conventionalfillers, such as organic microparticles, inorganic microparticles ofmetal oxides or metals, and organic-inorganic composite microparticles.Further, the fillers can be porous microparticles, hollowmicroparticles, capsulate microparticles or particles of compoundshaving a lamellar structure in which a low molecular weight compound isintercalated. Especially useful are microparticles of metal oxides, suchas alumina, silica, titanium oxide and zeolite; latex microparticlesformed of a polystyrene-polybutadiene copolymer; highly crystallinecellulose; and natural organic microparticles and fibers, such as ahighly crystalline cellulose nanofiber produced by an organism.

The back film used in the present invention may be subjected to aphysical treatment or chemical treatment so as to improve the adhesionof the back film to the photosensitive resin composition layer or theadhesive agent layer. With respect to the physical treatment, there canbe mentioned a sand blast method, a wet blast method (in which a liquidsuspension of microparticles is sprayed), a corona discharge treatment,a plasma treatment and an UV light irradiation or vacuum UV lightirradiation. With respect to the chemical treatment, there can bementioned a treatment with a strong acid or strong alkali, an oxidationagent or a coupling agent.

The thus obtained shaped photosensitive resin composition iscrosslink-cured by light or electron beam irradiation to obtain aprinting element. The photosensitive resin composition can also becrosslink-cured by light or electron beam irradiation while shaping thephotosensitive resin composition. Alternatively, the crosslink-curing ofthe resin composition can be performed by heating instead of light orelectron beam irradiation. However, it is preferred to perform thecrosslink-curing with light since a simple apparatus can be used, and aprinting element having a uniform thickness can be obtained. Withrespect to the light source used for curing, there can be mentioned ahigh pressure mercury lamp, an ultra-high pressure mercury lamp, anultraviolet fluorescent lamp, a carbon arc lamp and a xenon lamp. Thecuring of the resin composition can be also performed by any otherconventional methods for curing a resin composition. The photo-curingcan be performed by irradiating lights of different light sources incombination.

The thickness of the laser engravable printing element of the presentinvention can be appropriately selected depending on the use of theprinting element. When the printing element is used for producing aprinting plate, the thickness of the printing element is generally inthe range of from 0.1 to 15 mm. Further, the printing element can be amulti-layered printing element comprising a plurality of layers made ofdifferent materials.

Accordingly, in still another aspect of the present invention, there isprovided a multi-layered, laser engravable printing element comprising aprinting element layer and at least one elastomer layer provided belowthe printing element layer. The multi-layered, laser engravable printingelement of the present invention comprises a printing element layerwhich is made of the above-mentioned printing element of the presentinvention, and at least one elastomer layer provided below the printingelement layer. In general, the depth of the laser engraving in theprinting element layer (that is, the thickness of the portion which isremoved by laser engraving) is 0.05 mm to several millimeters. Theportion of the printing element under the engraved portion can be madeof a material other than the photosensitive resin composition of thepresent invention. The above-mentioned elastomer layer which functionsas a cushion layer has a Shore A hardness of from 20 to 70, preferablyfrom 30 to 60. When the Shore A hardness of the elastomer layer is inthe above-mentioned range, the elastomer layer is capable of changingits shape appropriately so as to maintain the printing quality of theprinting plate. When the Shore A hardness exceeds 70, such an elastomerlayer is incapable of functioning as a cushion layer.

There is no particular limitation with respect to an elastomer used as araw material for the elastomer layer so long as the elastomer has rubberelasticity. The elastomer layer may contain components other than anelastomer so long as the elastomer layer has a Shore A hardness in theabove-mentioned range. As elastomers usable as raw materials for theelastomer layer, there can be mentioned a thermoplastic elastomer, aphotocurable elastomer, a thermocurable elastomer and a porous elastomerhaving micropores having a size of nanometer level. From the viewpointof ease in producing a printing plate having a shape of a sheet orcylinder, it is preferred that the elastomer layer is produced byphotocuring a resin which is in a liquid state at room temperature (thatis, a raw material which becomes an elastomer after being photocured).

Specific examples of thermoplastic elastomers used for producing thecushion layer include styrene thermoplastic elastomers, such as SBS(polystyrene-polybutadiene-polystyrene), SIS (polystyrene-polyisoprene-polystyrene) and SEBS(polystyrene-polyethylene/polybutyrene-polystyrene); olefinthermoplastic elastomers; urethane thermoplastic elastomers; esterthermoplastic elastomers; and amide thermoplastic elastomers.

As the photocurable elastomers, there can be mentioned a mixtureobtained by mixing the above-mentioned thermoplastic elastomer with aphotopolymerizable monomer, a plasticizer, a photopolymerizationinitiator and the like; and a liquid composition obtained by mixing aplastomer resin with a photopolymerizable monomer, a photopolymerizationinitiator and the like.

In the present invention, differing from the production of a printingplate using a conventional printing plate, in which a precise mask imageshould be formed on the printing element using light, the resincomposition is cured by exposing the whole surface of the shaped articleof the resin composition to light and, thus, it is not necessary to usea material having properties which are conventionally needed to formprecise pattern on the printing element. Therefore, so long as the resincomposition exhibits a satisfactory level of mechanical strength, thereis a freedom of choice with respect to the raw materials used forproducing the resin composition.

In addition to the elastomers mentioned above, it is also possible touse vulcanized rubbers, organic peroxides, primary condensates ofphenolic resin, quinone dioxime, metal oxides and non-vulcanizedrubbers, such as thiourea. Further, it is also possible to use anelastomer obtained by three dimensionally crosslinking a telechelicliquid rubber by using a curing agent therefor.

There is no particular limitation with respect to the thickness of theelastomer layer, but it is generally in the range of from 0.05 mm to 10mm. With respect to the number of the elastomer layers, there is noparticular limitation, but it is generally one or two. For example,first elastomer layer having high resistance to ink can be providedbelow the printing element layer, and second elastomer layer having alower resistance to ink but having a higher cushioning properties can beprovided below the first elastomer layer. In the production of amulti-layered printing element, a back film can be formed either belowthe elastomer layer or in between the printing element layer and theelastomer layer.

In addition, a modifier layer can be provided on the surface of thelaser engravable printing element of the present invention to therebydecrease the surface tack and improve the ink wettability of theprinting plate. Examples of modifier layers include a coating formed bya surface treatment with a compound, such as a silane coupling agent anda titanium coupling agent, which reacts with hydroxyl groups present onthe surface of the printing element; and a polymer film containingporous inorganic particles.

Widely used silane coupling agent is a compound having in the moleculethereof a functional group which is highly reactive with hydroxyl groupspresent on the surface of a substrate. Examples of such functionalgroups include a trimethoxysilyl group, a triethoxysilyl group, atrichlorosilyl group, a diethoxysilyl group, a dimethoxysilyl group, adimonochlorosilyl group, a monoethoxysilyl group, a monomethoxysilylgroup and a monochlorosilyl group. At least one of these functionalgroups is present in each molecule of the silane coupling agent and themolecule is immobilized on the surface of a substrate by the reactionbetween the functional group and the hydroxyl groups present on thesurface of the substrate. Further, the silane coupling agent used in thepresent invention may contain a compound having in the molecule thereofat least one functional group selected from the group consisting of anacryloyl group, a methacryloyl group, an amino group containing anactive hydrogen, an epoxy group, a vinyl group, a perfluoroalkyl groupand a mercapto group, and/or a compound having a long chain alkyl groupas a reactive functional group.

Examples of titanium coupling agents include isopropyltriisostearoyltitanate, isopropyltris(dioctylpyrophosphate) titanate,isopropyltri(N-aminoethyl-aminoethyl) titanate,tetraoctylbis(di-tridecyl-phosphite) titanate,tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl)phosphite titanate,bis(octyl-pyrophosphate)oxyacetate titanate,bis(dioctylpyro-phosphate)ethylene titanate, isopropyltrioctanoyltitanate, isoproyldimethacrylisostearoyl titanate,isopropyltridodecylbenzenesulfonyl titanate, isopropylisostearoyldiacryltitanate, isopropyltri(dioctylsulfate) titanate, isopropyltricumylphenyltitanate and tetraisopropylbis(dioctylphosphite) titanate.

When the coupling agent molecule which is immobilized on the surface ofthe printing plate has a polymerizable reactive group, after theimmobilization of the coupling agent, the coupling agent may becross-linked by irradiation with light, heat or electron beam to therebyform a stronger coating.

Hereinbelow, explanations are made on the methods for performing acoupling agent treatment. If desired, the above-mentioned coupling agentmay be diluted with a mixture of water and alcohol or a mixture ofaqueous acetic acid and alcohol, to thereby obtain a coupling agentsolution. The concentration of the coupling agent in the solution ispreferably 0.05 to 10.0% by weight. The coupling agent solution isapplied to the surface of the printing element or the printing plateafter laser engraving, to thereby form a coating. There is no particularlimitation with respect to the method for applying the coupling agentsolution. For example, the application of the coupling agent solutionmay be performed by an immersing method, a spraying method, a rollcoating method or a coating method using a brush. There is no particularlimitation with respect to the coating temperature and the coating time,but it is preferred that the coating is performed at 5 to 60° C. for 0.1to 60 seconds. It is preferred that the drying of the coupling agentsolution layer formed on the surface of the printing element or theprinting plate is performed by heating, and the preferred heatingtemperature is 50 to 150° C.

Before treating the surface of the printing element or printing platewith a coupling agent, the surface of the printing element or printingplate may be irradiated with a xenon excimer lamp (that is, vacuumultraviolet light which has a wavelength of not more than 200 nm) orexposed to a high energy atmosphere (such as plasma), to therebygenerate hydroxyl groups on the surface of the printing element orprinting plate and immobilize the coupling agent at high density on thesurface of the printing element or printing plate.

When a printing element layer containing the particulate inorganicporous material is exposed at the surface of a printing plate, such aprinting plate may be treated under a high energy atmosphere, such asplasma, so as to etch the surface resin composition layer slightly, thusforming minute concave-convex portions on the surface. This treatmentmay decrease the surface tack and improve the ink wettability of theprinting plate because the treatment enables the particulate inorganicporous material to absorb ink more easily.

In a laser engraving process, a desired image is converted into digitaldata, and a relief pattern (corresponding to the desired image) isformed on the printing element by controlling a laser irradiationapparatus by a computer having the above-mentioned digital data. Thelaser used for the laser engraving may be any type of laser so long asthe laser comprises a light having a wavelength which can be absorbed bythe printing element. For performing the laser engraving quickly, it ispreferred that the output of the laser is as high as possible.Specifically, lasers having an oscillation in an infrared ornear-infrared range, such as a carbon dioxide laser, a YAG laser, asemiconductor laser and a fiber laser, are preferred. Further,ultraviolet lasers having an oscillation in a ultraviolet light range,such an excimer laser, a YAG laser tuned to the third or fourthharmonics and a copper vapor laser, may be used for an abrasiontreatment (which breaks the linkages in the organic compounds) andhence, are suitable for forming precise patterns. In addition, it isalso possible to use lasers having a very high spinodal output, such asa femtosecond laser. The laser irradiation may be either a continuousirradiation or a pulse irradiation. In general, a resin absorbs a lighthaving a wavelength around 10 μm. Therefore, when a carbon dioxide laserhaving an oscillation wavelength around 10 μm is used, there is no needto add a component for facilitating the absorption of the laser beam.However, when a YAG laser, a semiconductor laser, a fiber laser and thelike which have an oscillation wavelength around 1 μm are used, sincemost organic compounds do not absorb light having a wavelength around 1μm, it is necessary to add a component, such as a dye or a pigment, forfacilitating the absorption of a laser beam. Examples of such dyesinclude a poly(substituted)-phthalocyanine compound and a metal-containing phthalocyanine compound, a cyanine compound, a squaliliumdye, a chalcogenopyryloallylidene dye, a chloronium dye, a metalthiolate dye, a bis(chalcogenopyrylo)polymethene dye, an oxyindolidenedye, a bis(aminoaryl)polymethene dye, melocyanine dye and a quinoid dye.Examples of pigments include dark colored inorganic pigments, such ascarbon black, graphite, copper chromite, chromium oxide, cobalt chromiumaluminate and iron oxide; metal powders, such as iron, aluminum, copperand zinc, and doped metal powders which are obtained by doping any ofthe above-mentioned metal powders with Si, Mg, P, Co, Ni, Y or the like.These dyes and pigments can be used individually or in combination. Whena plurality of different dyes or pigments is used in combination, theycan be combined in any form. For example, different dyes or pigments maybe used in such a form as having a laminate structure. However, when aphotosensitive resin composition is cured by irradiation withultraviolet or visible light, for curing the printing element from theouter portion thereof through the inner portion thereof, it is preferredto avoid the use of a pigment and dye which absorb light having the samewavelength as that of light used for the curing of the resincomposition. The curing properties of a resin composition are influencedgreatly by the type of the photopolymerization initiator used, but theamount of a dye and/or pigment added to the photosensitive resincomposition is preferably not more than 1% by weight, more preferablynot more than 0.2% by weight, based on the weight of the resincomposition.

The laser engraving is performed in an atmosphere of oxygen-containinggas, generally in the presence of or under the flow of air; however, itcan be also performed in an atmosphere of carbon dioxide gas or nitrogengas. After completion of the laser engraving, powdery or liquid debrisgenerated in a small amount on the surface of the resultant reliefprinting plate may be removed by an appropriate method, such as washingwith a water containing a solvent or surfactant, high pressure sprayingof an aqueous detergent or spraying of a high pressure steam.

The printing element of the present invention can be advantageously usednot only for forming a relief pattern of a printing plate, but also forthe production of a stamp and seal; a design roll for embossing; arelief pattern for patterning a paste or ink used for producing anelectronic circuit, such as an insulating material, a resistivematerial, a conductive material and a semiconductive material (includingan organic semiconductive material); a relief pattern for mold used forproducing potteries; a relief pattern for display in an advertisement orindicator; and molds for various molded articles.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in more detail withreference to the following Examples and Comparative Examples, but theyshould not be construed as limiting the scope of the present invention.

Resins having a polymerizable unsaturated group, which are used in theExamples and the Comparative Examples, were synthesized in the followingReference Examples.

With respect to each of the polymerizable unsaturated group-containingresins produced in the Reference Examples, the number average molecularweight and average number of the polymerizable unsaturated group permolecule were determined by the following methods.

Number average molecular weight: The number average molecular weight ofa resin was measured by means of a high performance GPC apparatus(HLC-8020; manufactured and sold by Tosoh Corporation, Japan) and apolystyrene packed column (tradename: TSKgel GMHXL; manufactured andsold by Tosoh Corporation, Japan) wherein tetrahydrofuran (THF) was usedas a carrier. The column temperature was maintained at 40° C. A THFsolution containing 1% by weight of a resin was used as a sample and 10μl of the sample was charged to the GPC apparatus. A UV absorptiondetector was used as a detector and a light having a wavelength of 254nm was used as a monitoring light.

Average number of polymerizable unsaturated group per molecule:

In each of the Reference Examples, an intermediate resin product havingtwo terminal hydroxyl groups (e.g., a resin product produced by reactinga diol compound and tolylene diisocyanante) was provided and, then, afinal resin product having a methacryl group as a polymerizableunsaturated group was produced, for example, by adding2-methacryloyloxyisocyanate to the intermediate resin product, tothereby react the terminal hydroxyl groups of the intermediate resinproduct with an isocyanate group of 2-methacryloyloxyisocyanate. Inorder to measure the number of the Ipolymerizable unsaturated group permolecule of the final resin product, the above-mentioned intermediateresin product and final resin product was individually dissolved in adeuterated chloroform, and the resultant solutions were analyzed by NMRspectroscopy. The NMR spectroscopy was performed using α500 type NMRapparatus (detection frequency: 500 MHz) (manufactured and sold by JEOLLtd., Japan). The molecular structures of the intermediate resin productand final resin product were determined by analyzing the NNR spectrum.Specifically, the unreacted hydroxyl group and methacryl group of thefinal resin product were identified, and the molar ratio (R) of theunreacted hydroxyl group to the methacryl group was calculated from thesignal integral ratio of the NMR spectrum. Using the thus obtained Rvalue, the average number of the polymerizable unsaturated group permolecule was calculated.

Further, in each of Reference Examples 1 to 9, the change in the amountof the isocyanate group (i.e., isocyanate group of the reaction productof a reaction between a polyol and a diisocyanate in each of ReferenceExamples 1, 2 and 4, or isocyanate group of 2-methacryloyloxyisocyanatein each of Reference Examples 3, and 5 to 9) was monitored by means of aFT-IR (1640 type infrared Foulier transform spectrometer) (manufacturedand sold by Perkin Elmer Inc., U.S.A.) to thereby determine the reactiontime for producing the final resin product.

REFERENCE EXAMPLE 1

To a separable flask (which had a capacity of 1 liter and was equippedwith a thermometer, a stirrer and a reflux condenser) were added 500 gof polytetramethylene glycol (Mn: 1,830, OH value: 61.3) (manufacturedand sold by Asahi Kasei Kabushiki Kaisha, Japan) and 52.40 g of tolylenediisocyanate, and the resultant mixture was heated at 60° C. forapproximately 3 hours to perform a reaction, thereby obtaining areaction mixture. Subsequently, 25.24 g of 2-hydroxypropyl methacrylateand 31.75 g of polypropylene glycol monomethacrylate (Mn: 400) wereadded to the obtained reaction mixture, and the reaction was furthercontinued for 2 hours, thereby obtaining resin (I) having a terminalmethacryl group (the average number of methacryl group (polymerizableunsaturated group) per molecule was approximately 2) and having a numberaverage molecular weight of approximately 20,000. Resin (I) was aviscous fluid at 20° C. and it was a plastomer which changes a shapethereof in accordance with a force applied thereto and does not recoverthe original shape thereof after released from the force.

REFERENCE EXAMPLE 2

To a separable flask (which had a capacity of 1 liter and was equippedwith a thermometer, a stirrer and a reflux condenser) were added 500 gof polycarbonate diol (tradename: Kuraray Polyol C-2015N; manufacturedand sold by Kuraray Co., Ltd., Japan) (Mn: 2,000, OH value: 56.0) and49.86 g of tolylene diisocyanate, and the resultant mixture was heatedat 60° C. for approximately 3 hours to perform a reaction, therebyobtaining a reaction mixture. Subsequently, 26.63 g of 2-hydroxypropylmethacrylate and 35.27 g of polypropylene glycol monomethacrylate wereadded to the obtained reaction mixture, and the reaction was furthercontinued for 2 hours, thereby obtaining resin (II) having a terminalmethacryl group (the average number of methacryl group (polymerizableunsaturated group) per molecule was approximately 2) and having a numberaverage molecular weight of approximately 15,000. Resin (II) was aviscous fluid at 20° C. and it was a plastomer which changes a shapethereof in accordance with a force applied thereto and does not recoverthe original shape thereof after released from the force.

REFERENCE EXAMPLE 3

To a separable flask (which had a capacity of 1 liter and was equippedwith a thermometer, a stirrer and a reflux condenser) were added 500 gof polyisoprene polyol (tradename: LIR-506; manufactured and sold byKuraray Co., Ltd., Japan) (Mn: 16,400, OH value: 17.1) and 23.65 g of2-methacryloyloxyisocyanate, and the resultant mixture was heated at 60°C. for 7 hours to perform a reaction, thereby obtaining resin (III)having a terminal methacryl group (the average number of methacryl group(polymerizable unsaturated group) per molecule was approximately 5) andhaving a number average molecular weight of approximately 17,200. Resin(III) was a viscous fluid at 20° C. and it was a plastomer which changesa shape thereof in accordance with a force applied thereto and does notrecover the original shape thereof after released from the force.

REFERENCE EXAMPLE 4

To a separable flask (which had a capacity of 1 liter was equipped witha thermometer, a stirrer and a reflux condenser) were added 500 g ofpolytetramethylene glycol (Mn: 1,830, OH value: 61.3) (manufactured andsold by Asahi Kasei Kabushiki Kaisha, Japan) and 52.40 g of tolylenediisocyanate, and the resultant mixture was heated at 60° C. forapproximately 3 hours to perform a reaction, thereby obtaining areaction mixture. Subsequently, 6.2 g of 2-hydroxypropyl methacrylateand 7.9 g of polypropylene glycol monomethacrylate (Mn: 400) were addedto the obtained reaction mixture, and the reaction was further continuedfor 2 hours, followed by addition of 20 g of ethanol. The reaction wascontinued for 2 hours to thereby obtain resin (IV) having a terminalmethacryl group (the average number of polymerizable unsaturated group(methacryl group) per molecule was approximately 0.5) and having anumber average molecular weight of approximately 20,000. Resin (IV) wasa viscous fluid at 20° C. and it was a plastomer which changes a shapethereof in accordance with a force applied thereto and does not recoverthe original shape thereof after released from the force.

REFERENCE EXAMPLE 5

To a separable flask (which had a capacity of 1 liter and was equippedwith a thermometer, a stirrer and a reflux condenser) were added 447.24g of polycarbonate diol (tradename: PCDL L4672; manufactured and sold byAsahi Kasei Kabushiki Kaisha, Japan) (Mn: 1,990, OH value: 56.4) and30.83 g of tolylene diisocyanate, and the resultant mixture was heatedat 80° C. for approximately 3 hours to perform a reaction, therebyobtaining a reaction mixture. Subsequently, 14.83 g of2-methacryloyloxyisocyanate was added to the obtained reaction mixture,and the reaction was further continued for approximately 3 hours,thereby obtaining resin (V) having a terminal methacryl group (theaverage number of polymerizable unsaturated group (methacryl group) permolecule was approximately 2) and having a number average molecularweight of approximately 10,000. Resin (V) was a viscous fluid at 20° C.and it was a plastomer which changes a shape thereof in accordance witha force applied thereto and does not recover the original shape thereofafter released from the force.

REFERENCE EXAMPLE 6

To a separable flask (which had a capacity of 1 liter was equipped witha thermometer, a stirrer and a reflux condenser) were added 447.24 g ofpolycarbonate diol (tradename: PCDL L4672) (manufactured and sold byAsahi Kasei Kabushiki Kaisha, Japan) (Mn: 1,990, OH value: 56.4) and30.83 g of tolylene diisocyanante, and the resultant mixture was heatedat 80° C. for approximately 3 hours to perform a reaction, therebyobtaining a reaction mixture. Subsequently, 7.42 g of2-methacryoyloxyisocyanate was added to the obtained reaction mixture,and the reaction was continued for approximately 3 hours, therebyobtaining resin (VI) having a terminal methacryl group (the averagenumber of polymerizable unsaturated group (methacryl group) per moleculewas approximately 1) and having a number average molecular weight ofapproximately 10,000. Resin (VI) was a viscous fluid at 20° C. and itwas a plastomer which changes a shape thereof in accordance with a forceapplied thereto and does not recover the original shape thereof afterreleased from the force.

REFERENCE EXAMPLE 7

To a separable flask (which had a capacity of 1 liter and was equippedwith a thermometer, a stirrer and a reflux condenser) were added 449.33g of polycarbonate diol (tradename: PCDL L4672; manufactured and sold byAsahi Kasei Kabushiki Kaisha, Japan) (Mn: 1,990, OH value: 56.4) and12.53 g of tolylene diisocyanante, and the resultant mixture was heatedat 80° C. for approximately 3 hours to perform a reaction, therebyobtaining a reaction mixture. Subsequently, 47.77 g of2-methacryoyloxyisocyanate was added to the obtained reaction mixture,and the reaction was further continued for approximately 3 hours,thereby obtaining resin (VII) having a terminal methacryl group (theaverage number of polymerizable unsaturated group (methacryl group) permolecule was approximately 2) and having a number average molecularweight of approximately 3,000. Resin (VII) was a viscous fluid at 20° C.and it was a plastomer which changes a shape thereof in accordance witha force applied thereto and does not recover the original shape thereofafter released from the force.

REFERENCE EXAMPLE 8

To a separable flask (which had a capacity of 1 liter and was equippedwith a thermometer, a stirrer and a reflux condenser) were added 449.33g of polycarbonate diol (tradename: PCDL L4672; manufactured and sold byAsahi Kasei Kabushiki Kaisha, Japan) (Mn: 1,990, OH value: 56.4) and12.53 g of tolylene diisocyanante, and the resultant mixture was heatedat 80° C. for approximately 3 hours to perform a reaction, therebyobtaining a reaction mixture. Subsequently, 23.89 g of2-methacryloyloxyisocyanate was added to the reaction mixture, and thereaction was further continued for approximately 3 hours, therebyobtaining resin (VIII) having a terminal methacryl group (the averagenumber of polymerizable unsaturated group (methacryl group) per moleculewas approximately 1) and having a number average molecular weight ofapproximately 3,000. Resin (VIII) was a viscous fluid at 20° C. and itwas a plastomer which changes a shape thereof in accordance with a forceapplied thereto and does not recover the original shape thereof afterreleased from the force.

REFERENCE EXAMPLE 9

A separable flask (which had a capacity of 1 liter and was equipped witha thermometer, a stirrer and a reflux condenser) were added 500.00 g oftripropylene glycol (Mn: 192) (manufactured and sold by Tokyo KaseiKogyo Co., Ltd., Japan) and 283.52 g of tolylene diisocyanante, and theresultant mixture was heated at 80° C. for approximately 3 hours toperform a reaction, thereby obtaining a reaction mixture. Subsequently,75.98 g of 2-methacryloyloxyisocyanate was added to the reactionmixture, and the reaction was further continued for approximately 3hours to thereby obtain resin (IX) having a terminal methacryl group(the average number of polymerizable unsaturated group (methacryl group)per molecule was approximately 0.5) and having a number averagemolecular weight of approximately 800. Resin (IX) was a viscous fluid at20° C. and it was a plastomer which changes a shape thereof inaccordance with a force applied thereto and does not recover theoriginal shape thereof after released from the force.

In the following Examples and Comparative Examples, properties of aphotosensitive resin composition were evaluated and measured as follows.

(1) Laser Engraving

Laser engraving was performed by means of a carbon dioxide laserengraving apparatus (tradename: TYP STAMPLAS SN 09; manufactured andsold by Baasel Lasertech, Germany). The laser engraved pattern includedportions corresponding to halftone dots (screen ruling=80 lpi (lines perinch), and total area of halftone dots=approximately 10%, based on thehalftone area of a print obtained using the engraved pattern), 500μm-wide relief lines (convex lines) and 500 μm-wide reverse lines(grooves). When the laser engraving is performed so that the engravingdepth becomes large, a problem arises wherein a satisfactorily largearea of the top portion of a precise halftone relief pattern cannot beobtained, so that the destruction of the portions corresponding tohalftone dots occurs and the printed dots become unclear. For preventingthis problem, the laser engraving was performed with the engraving depthof 0.55 mm.

(2) Amount of Wiping Needed to Remove the Debris and the Relative Amountof the Residual Debris

Debris on the printing element after laser engraving was wiped away witha nonwoven fabric (tradename: BEMCOT M-3; manufactured and sold by AsahiKasei Kabushiki Kaisha, Japan) which was impregnated with ethanol oracetone. The amount of wiping needed to remove the debris was defined asthe number of times the wiping was performed to remove the viscousliquid debris generated during the laser engraving. A large amount ofwiping means that a large amount of liquid debris was formed on theprinting plate. It is preferred that the amount of wiping needed toremove the debris is not more than 5 times, more advantageously not morethan 3 times.

Further, the weight of a printing element before laser engraving, theweight of the printing element immediately after the laser engraving andthe weight of a relief printing plate after wiping were measured. Therelative amount of the residual debris was calculated in accordance withthe following formula:

$\frac{\begin{matrix}\left( {{Weight}\mspace{14mu}{of}\mspace{14mu} a\mspace{14mu}{printing}\mspace{14mu}{element}\mspace{14mu}{immediately}} \right. \\{\left. {{after}\mspace{14mu}{laser}\mspace{14mu}{engraving}} \right) - \left( {{Weight}\mspace{14mu}{of}\mspace{14mu} a} \right.} \\\left. {{relief}\mspace{14mu}{printing}\mspace{14mu}{plate}\mspace{14mu}{after}\mspace{14mu}{wiping}} \right)\end{matrix}}{\begin{matrix}\left( {{Weight}\mspace{14mu}{of}\mspace{14mu} a\mspace{14mu}{printing}\mspace{14mu}{element}\mspace{14mu}{before}} \right. \\{\left. {{laser}\mspace{14mu}{engraving}} \right) - \left( {{Weight}\mspace{14mu}{of}\mspace{14mu} a\mspace{14mu}{relief}} \right.} \\\left. {{printing}\mspace{14mu}{plate}\mspace{14mu}{after}\mspace{14mu}{wiping}} \right)\end{matrix}} \times 100$It is advantageous when a printing plate has the residual debris in anamount of not more than 15% by weight, preferably not more than 10% byweight.(3) Tack on the Surface of a Relief Printing Plate

Tack on the surface of a relief printing plate after wiping was measuredby means of a tack tester (manufactured and sold by Toyo SeikiSeisaku-Sho Ltd., Japan). Specifically, an aluminum ring having a radiusof 50 mm and a width of 13 mm was attached to a smooth portion of arelief printing plate (test specimen) at 20° C. so that the aluminumring stood vertically on the specimen. A load of 0.5 kg was applied tothe aluminum ring for 4 seconds. Subsequently, the aluminum ring waspulled at a rate of 30 mm per minute and the resisting force at the timeof the detachment of the aluminum ring was measured by means of apush-pull gauge. The larger the resisting force, the larger the surfacetack (tackiness) and the adhesive strength of the specimen. It isadvantageous when the surface tack of a printing plate is not more than150 N/m, preferably not more than 100 N/m.

(4) Evaluation of Portions of a Relief Pattern Which Correspond toHalftone Dots

With respect to the laser engraved printing plate (having a reliefpattern formed thereon) obtained by the method of item (1) above, theportions of the relief pattern which correspond to the halftone dots(screen ruling=80 lpi (lines per inch), and total area of halftonedots=approximately 10%, based on the halftone area of a print obtainedusing the engraved pattern) were observed under an electron microscopewith a magnification of 200 to 500. It is advantageous when the portionsof the relief pattern which correspond to the halftone dots have a coneshape or cone-like shape (i.e., truncated cone in which the apex of acone is removed so that the plane at the top portion of the resultantcone is parallel to the base of the cone).

(5) Pore Volume, Average Pore Diameter and Specific Surface Area of aPorous or Non-Porous Material

2 g of a porous or non-porous material as a sample was placed in a testtube and vacuum-dried for 12 hours by means of a pretreatment apparatusat 150° C. under 1.3 Pa or less. The pore volume, average pore diameterand specific surface area of the dried porous or non-porous materialwere measured by means of “Autosorb-3MP” (manufactured and sold byQuantachrome Instruments, U.S.A.), wherein nitrogen gas was adsorbed onthe porous or non-porous material in an atmosphere cooled by liquidnitrogen. Specifically, the specific surface area was calculated by theBET formula. With respect to the pore volume and average pore diameter,a cylindrical model was postulated from the adsorption isotherm duringthe elution of nitrogen, and the pore volume and average pore diameterwere calculated by the BJH (Brrett-Joyner-Halenda) method which is aconventional method for analyzing pore distribution.

(6) Ignition Loss of the Porous or Non-Porous Material

The weight of a sample of a porous or nonporous material was measuredand recorded. Subsequently, the sample was heated using a hightemperature electric furnace (FG31 type; manufactured and sold by YamatoScientific Co., Ltd., Japan) in air at 950° C. for 2 hours. Thedifference in the weight of the sample as between before and after theheating was defined as the ignition loss.

(7) Viscosity

The viscosity of a resin composition was measured by means of a B typeviscometer (B8H type; manufactured and sold by Kabushiki Kaisha TokyoKeiki, Japan) at 20° C.

EXAMPLES 1 TO 9 AND COMPARATIVE EXAMPLES 1 TO 4

In Examples 1 to 9 and Comparative Examples 1 to 4, resin compositionshaving formulations shown in Table 1 were produced as follows. InExamples 1 to 9 and Comparative Examples 1 to 4, resins (I) to (IX)(which were, respectively, produced in Reference Examples 1 to 9) and astyrene-butadiene copolymer (hereinafter, referred to as “SBS”)(tradename: Tufprene A; manufactured and sold by Asahi Kasei KabushikiKaisha, Japan) were used as resin (a); the acrylic esters shown in Table1 were used as organic compound (b); and inorganic porous material (c),photopolymerization initiator (d) and other additives which are shown inTable 1 were used. In each of Examples 1 to 9 and Comparative Examples 1to 4, in accordance with the formulation shown in Table 1, all of thecomponents were charged into a separable flask equipped with agitatingblades and a motor (tradename: Three One Motor), and the resultantmixture were agitated at 80° C. in the presence of air. The resultantmixture was cooled to 40° C. and allowed to stand still at 40° C. tothereby deaerate the mixture and obtain a resin composition. Thecharacteristics of organic compound (b) used in the Examples and theComparative Examples are shown in Table 2. As inorganic porous material(c), the following porous microparticulate silica products (eachmanufactured and sold by Fuji Silysia Chemical Ltd., Japan) were used:

C-1504 (tradename: SYLOSPHERE C-1504) (number average particle diameter:4.5 μm, specific surface area: 520 m²/g, average pore diameter: 12 nm,pore volume: 1.5 ml/g, ignition loss: 2.5% by weight, oil absorption:290 ml/100 g, and specific porosity (defined above): 780);

CH-4004 (tradename: SYLOPHOBIC 4004) (number average particle diameter:8.0 μm, specific surface area: 300 m²/g, average pore diameter: 17 nm,pore volume: 1.25 ml/g, ignition loss: 5.0% by weight, oil absorption:200 ml/100 g and specific porosity: 800); and

C-470 (tradename: SYLYSIA 470) (number average particle diameter: 14.1μm, specific surface area: 300 m²/g, average pore diameter: 17 nm, porevolume: 1.25 ml/g, ignition loss: 5.0% by weight, oil absorption: 180ml/100 g and specific porosity: 1410).

(The above-mentioned values of average pore diameter and oil absorptionare those described in the manufacturer's catalog. Other values wereobtained by the measurements conducted by the present inventors. Thespecific porosity was calculated by the above-mentioned method using thedensity (2 g/cm³) of each of the porous materials.)

The obtained resin composition was shaped into a sheet (thickness: 2.8mm) on a PET (polyethylene terephthalate) film. The shaped resin articlewas photo-cured by means of ALF type 213E exposure apparatus(manufactured and sold by Asahi Kasei Kabushiki Kaisha, Japan) and anultraviolet low pressure mercury lamp (“FLR20S-B-DU-37C/M”; manufacturedand sold by Toshiba Corporation, Japan) (emission wavelength: 350 to 400nm, peak wavelength: 370 nm). The exposure was performed for 10 minutesin vacuo, in which the upper surface of the sheet (on which a reliefpattern was to be formed) was exposed at 1000 mJ/cm² and the othersurface of the sheet was exposed at 500 mJ/cm², thereby obtaining aprinting element.

A relief pattern was engraved on the obtained printing element by meansof a carbon dioxide laser engraving apparatus, thereby obtaining arelief printing plate, and the obtained relief printing plate wasevaluated. The results are shown in Table 3.

Further, each of the resin compositions produced in the Examples and theComparative Examples was a liquid resin composition capable of plasticdeformation at 20° C., namely a plastomer. The viscosities of thephotosensitive resin compositions at 20° C. are shown in Table 4.

TABLE 1 Organic compound (b) Compound having an alicyclic functionalgroup Inorganic porous Polymerization Other Resin (a) or an aromaticmaterial (c) initiator (d)*³ additives*⁴ Type Amount*¹ Type Amount*¹functional group*² Type Amount*¹ Type Amount*¹ Type Amount*¹ Ex. 1 (I)100 LMA 6 none C-1504 5 DMPAP 0.6 BHT 0.5 PPMA 15 DEEHEA 25 TEGDMA 2TMPTMA 2 Comp. (II) 100 LMA 6 none None ″ ″ BHT 0.5 Ex. 1 PPMA 15 DEEHEA25 TEGDMA 2 TMPTMA 2 Ex. 2 (II) 100 LMA 6 none C-1504 5 ″ ″ ″ ″ PPMA 15LB 5 DEEHEA 25 TEGDMA 2 TMPTMA 2 Ex. 3 (III) 100 LMA 6 none ″ ″ ″ ″ BHT0.5 PPMA 15 DEEHEA 25 TEGDMA 2 TMPTMA 2 Comp. SBS 100 LMA 6 none none ″″ ″ ″ Ex. 2 PPMA 15 DEEHEA 25 TEGDMA 2 TMPTMA 2 Comp. (IV) 100 LMA 6none C-1504 7 ″ ″ ″ ″ Ex. 3 PPMA 15 DEEHEA 25 TEGDMA 2 TMPTMA 2 Ex. 4(V) 100 BZMA 25 88 ″ 5 ″ ″ ″ ″ CHMA 19 BDEGMA 6 Ex. 5 (VI) 100 CHMA 3872 ″ 7 ″ ″ ″ ″ BDEGMA 12 TMPTMA 3 Ex. 6 (VII) 100 BZMA 50 100 ″ 5 ″ ″ ″″ Ex. 7 (VIII) 100 PEMA 47 94 ″ 7 ″ ″ ″ ″ TMPTMA 3 Comp. (IX) 100 PEMA47 ″ ″ ″ ″ ″ ″ ″ Ex. 4 TMPTMA 3 Ex. 8 (VI) 100 BZMA 25 88 C-4004 5 ″ ″ ″″ CHMA 19 BDEGMA 6 Ex. 9 (VI) 100 BZMA 25 ″ C-470 5 ″ ″ ″ ″ CHMA 19BDEGMA 6 *¹Amounts of the components of the resin composition areindicated in terms of parts by weight, relative to 100 parts be weightof resin (A). *²Among organic compounds (b) used in the Examples and theComparative Examples, BZMA, CHMA and PEMA are compounds having at leastone functional group selected from the group consisting of an alicyclicfunctional group and an aromatic functional group. *³DMPAP represents2,2-dimethoxy-2-phenylacetophene. *⁴BHT represents2,6-di-t-butylacetophene and LB represents lauric acid n-butyl ester.

TABLE 2 Number of Number polymerizable Abbreviations average unsaturatedused in molecular group per Table 1 Nomenclature weight*¹ molecule*² LMAlauryl methacrylate 254 1 PPMA propylene glycol mono- 400 1 methacrylateDEEHEA diethylene glycol-2-ethyl- 286 1 hexylmethyl acrylate TEGDMAtetraethylene glycol 330 2 dimethacrylate TMPTMA trimethylol propane 3393 trimethacrylate BZMA benzyl methacrylate 176 1 CHMA cyclohexylmethacrylate 167 1 BDEGMA buthoxy ethylene glycol 230 1 methacrylatePEMA phenoxyethyl methacrylate 206 1 *¹When organic compound (b) wasanalyzed by GPC, the chromatogram showed a single peak having apolydispersibility of less than 1.1. Accordingly, the number averagemolecular weight was determined by mass spectrometric analysis. *²Valueobtained by NMR.

TABLE 3 Amount of Relative wiping needed Tack on amount of to remove thethe relief residual debris printing Shape of relief debris (BEMCOT plateafter portions corresponding (% by impregnated wiping to weight) withethanol) (N/m) halftone dots Ex. 1 7.8 ≦3 49 Excellent cone shape Comp.11.0 10 167 Excellent cone Ex. 1 shape Ex. 2 6.0 ≦3 88 Excellent coneshape Ex. 3 8.4 ≦3 83 Excellent cone shape Comp. 16.6   30< 69 Deformedand Ex. 2 unclear dots Comp. 8.2 ≦3 118 Deformed and Ex. 3 slightlyunclear dots Ex. 4 5.1 ≦3 78 Excellent cone shape Ex. 5 3.5 ≦3 93Excellent cone shape Ex. 6 5.0 ≦3 83 Excellent cone shape Ex. 7 4.3 ≦393 Excellent cone shape Comp. 10.0 ≦3 196 Deformed and Ex. 4 uncleardots Ex. 8 8.2 ≦3 125 Excellent cone shape Ex. 9 5.2 ≦3 118 Excellentcone shape

TABLE 4 Viscosity of the photosensitive resin composition Pa · s (20°C.) Example 1 3000 Example 2 2830 Example 3 700 Example 4 2100 Example 52500 Example 6 80 Example 7 95 Example 8 2000 Example 9 2100 Comparative2340 Example 1 Comparative —(solid) Example 2 Comparative 2700 Example 3Comparative 9.5 Example 4

EXAMPLE 10

The photosensitive resin composition produced in Comparative Example 2was shaped into a sheet having a thickness of 2 mm and the shaped resincomposition was photocured in the same manner as in Example 1 to obtainan elastomer sheet. The obtained elastomer sheet was used as anelastomer layer (cushion layer) of the below-mentioned multi-layeredprinting element. The Shore A hardness of the elastomer sheet was 55.

On the above-obtained elastomer sheet was coated the photosensitiveresin composition produced in Example 4 (i.e., photosensitive resincomposition containing resin (V)) so as to form a coating having athickness of 0.8 mm. The photosensitive resin coating was photocured inthe same manner as in Example 4 to thereby obtain a multi-layeredprinting element.

A relief pattern was engraved on the obtained multi-layered printingelement by means of a carbon dioxide laser engraving apparatus, therebyobtaining a relief printing plate, and the obtained relief printingplate was evaluated. The relative amount of residual debris was 5.7% byweight, the amount of wiping needed to remove the debris was not morethan 3 times and the tack on the relief printing plate after wiping was83 N/m. The portions of the relief pattern, which correspond to halftonedots, had an excellent cone shape.

COMPARATIVE EXAMPLE 5

A printing element was produced in substantially the same manner as inExample 4 except that organic porous spherical particles were usedinstead of inorganic porous material (c). The organic porous sphericalparticles were crosslinked polystyrene particles having a number averageparticle diameter of 8 μm, a specific surface area of 200 m²/g, anaverage pore diameter of 50 nm and a pore volume of 2.5 ml/g.

When a relief pattern was engraved on the obtained printing element bymeans of a carbon dioxide laser engraving apparatus, a large amount ofviscous liquid debris was generated and the amount of wiping needed toremove the debris became more than 30 times. It is considered that themelting and deformation of the organic porous spherical particles werecaused by the laser irradiation and the organic porous sphericalparticles were incapable of maintaining the porous structure thereof.

COMPARATIVE EXAMPLE 6

A photosensitive resin composition was produced in substantially thesame manner as in Example 4 except that 0.2% by weight of carbon black(tradename: Seast SP, SRF-LS; manufactured and sold by Tokai Carbon Co.,Ltd., Japan) (average particle diameter: 95 nm, specific surface area:23 m²/g, average pore diameter: less than 1 nm) was used instead ofinorganic porous material (c). The specific porosity of carbon black was0.8, wherein the specific porosity was calculated using the spacebetween the layers (which was determined by X-ray diffraction analysis)as an average pore diameter and 2.25 g/cm³ as the density.

An attempt was made to produce a printing element from theabove-mentioned photosensitive resin composition in the same manner asin Example 4. However, even when the irradiation dose was increased to6000 mJ/cm², only the surface portion having a thickness of about 0.2 mmcould be cured. The resultant semi-cured resin composition could not beused as a laser engravable printing element.

The cured portion of the resin composition (thickness of about 0.2 mm)was separated from the uncured portion of the resin composition, therebyobtaining a resin plate. The surface of the resin plate, on which theuncured liquid resin composition remains, was cured by UV rayirradiation, thereby obtaining a printing element.

A relief pattern was engraved on the obtained printing element by meansof a carbon dioxide laser engraving apparatus, wherein the engravingdepth was 0.1 mm. The engraving debris formed during the laser engravingwas a viscous liquid. It is considered that the addition of carbon blackto the resin composition lead to an unsatisfactory curing of the innerportion of the printing element. Such a phenomenon is frequentlyobserved in the case where it is attempted to photocure a photosensitiveresin composition to which microparticles having a high ability toabsorb UV light have been added. Further, when the amount of carbonblack added to the resin composition is small as in the case ofComparative Example 6, the satisfactory removal of the liquid debris bythe carbon black cannot be expected.

COMPARATIVE EXAMPLE 7

A printing element was produced in substantially the same manner as inExample 4 except that a substantially nonporous material, namelyaluminosilicate (tradename: Silton AMT08L; manufactured and sold byMizusawa Industrial Chemicals, Ltd.), was used instead of inorganicporous material (c). The nonporous material had a pore volume of 0.08ml/g, an average pore diameter of 0.9 μm and a specific surface area of21 m²/g, and exhibited an oil absorption of 60 ml/100 g. The specificporosity (obtained by the above-mentioned method using the density (2g/cm³) of the material) was 6.3.

When a relief pattern was engraved on the obtained printing element bymeans of a carbon dioxide laser engraving apparatus, a large amount ofviscous liquid debris was generated and the amount of wiping needed toremove the debris became more than 10 times. Although the shape of theportions of the relief pattern which correspond to the halftone dots wasa cone, the tack on the relief printing plate after wiping was as highas 280 N/m.

COMPARATIVE EXAMPLE 8

A printing element was produced in substantially the same manner as inExample 4 except that a substantially nonporous material, namelyaluminosilicate (tradename: Silton AMT25, manufactured and sold byMizusawa Industrial Chemicals, Ltd.), was used instead of inorganicporous material (c). The substantially nonporous material had a porevolume of 0.006 ml/g, an average pore diameter of 2.9 μm and a specificsurface area of 2.3 m²/g, and exhibited an oil absorption of 40 ml/100g. The specific porosity (which was obtained by the above-mentionedmethod using the density (2 g/cm³) of the material) was 2.2.

When a relief pattern was engraved on the obtained printing element bymeans of a carbon dioxide laser engraving apparatus, a large amount ofviscous liquid debris was generated and the amount of wiping needed toremove the debris became more than 10 times. Although the shape of theportions of the relief pattern which correspond to the halftone dots wasa cone, the tack on the relief printing plate after wiping was as highas 300 N/m.

COMPARATIVE EXAMPLE 9

A printing element was produced in substantially the same manner as inExample 4 except that a substantially nonporous material, namely sodiumcalcium aluminosilicate (tradename: Silton JC50, manufactured and soldby Mizusawa Industrial Chemicals, Ltd.), was used instead of inorganicporous material (c). The substantially nonporous material had a porevolume of 0.02 ml/g, an average pore diameter of 5.0 μm and a specificsurface area of 6.7 m²/g, and exhibited an oil absorption of 45 ml/100g. The specific porosity (obtained by the above-mentioned method usingthe density (2 g/cm³) of the material) was 11.

When a relief pattern was engraved on the obtained printing element bymeans of a carbon dioxide laser engraving apparatus, a large amount ofviscous liquid debris was generated and the amount of wiping needed toremove the debris became more than 10 times. Although the shape of theportions of the relief pattern which correspond to the halftone dots wasa cone, the tack on the relief printing plate after wiping was as highas 260 N/m.

INDUSTRIAL APPLICABILITY

By the use of the photosensitive resin composition of the presentinvention, it becomes possible to produce a printing element which notonly has high uniformity in thickness and high dimensional precision,but also generates only a small amount of debris during laser engravingof the printing element. Further, the produced printing element isadvantageous in that a precise image can be formed on the printingelement by laser engraving and the resultant image-bearing printingplate has small surface tack. Such a printing element can beadvantageously used for forming a relief pattern of a flexographicprinting plate, a design roll for embossing, a relief pattern forprinting tiles and the like, and patterning of a conductive material, asemiconductive material and an insulating material for producing anelectronic circuit.

1. A photosensitive resin composition for forming a laser engravableprinting element, comprising: (a) 100 parts by weight of a resin whichis a plastomer at 20° C., wherein said resin has a number averagemolecular weight of from 1,000 to 100,000 and has a polymerizableunsaturated group in an amount such that the average number of thepolymerizable unsaturated group per molecule is at least 0.7, (b) 5 to200 parts by weight, relative to 100 parts by weight of said resin (a),of an organic compound having a number average molecular weight of lessthan 1,000 and having at least one polymerizable unsaturated group permolecule, and (c) 1 to 100 parts by weight, relative to 100 parts byweight of said resin (a), of an inorganic porous material.
 2. Thephotosensitive resin composition according to claim 1, wherein saidinorganic porous material (c) has a number average particle diameter offrom 0.1 μm to 100 μm, an average pore diameter of from 1 nm to 1,000nm, and a pore volume of from 0.1 ml/g to 10 ml/g.
 3. The photosensitiveresin composition according to claim 1 or 2, wherein said resincomposition further comprises (d) a photopolymerization initiator. 4.The photosensitive resin composition according to claim 1 or 2, whereinat least 20% by weight of said organic compound (b) is a compound havingat least one functional group selected from the group consisting of analicyclic functional group and an aromatic functional group.
 5. Thephotosensitive resin composition according to claim 1 or 2, wherein saidinorganic porous material (c) has a specific surface area of from 10m^(2/)g to 1,500 m^(2/)g, and exhibits an oil absorption of from 10ml/100 g to 2,000 ml/100 g.
 6. The photosensitive resin compositionaccording to claim 1 or 2 for use in forming a relief printing element.7. A laser engravable printing element which is a cured photosensitiveresin composition having a shape of a sheet or cylinder, wherein saidlaser engravable printing element contains an inorganic porous material.8. A multi-layered, laser engravable printing element comprising aprinting element layer and at least one elastomer layer provided belowthe printing element layer, wherein said printing element layer is madeof the laser engravable printing element of claim 7 and said elastomerlayer has a Shore A hardness of from 20 to
 70. 9. The multi-layered,laser engravable printing element according to claim 8, wherein saidelastomer layer is produced by photocuring a resin which is in a liquidstate at room temperature.
 10. A laser engravable printing elementobtainable by a process comprising: shaping the photosensitive resincomposition according to claim 1 or 2 into a sheet or cylinder, andcrosslink-curing said photosensitive resin composition by light orelectron beam irradiation.
 11. A multi-layered, laser engravableprinting element comprising a printing element layer and at least oneelastomer layer provided below the printing element layer, wherein saidprinting element layer is made of the laser engravable printing elementof claim 10 and said elastomer layer has a Shore A hardness of from 20to
 70. 12. The multi-layered, laser engravable printing elementaccording to claim 11, wherein said elastomer layer is produced byphotocuring a resin which is in a liquid state at room temperature.